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1=> NAME 1NAME
2 AnyEvent - provide framework for multiple event loops 2 AnyEvent - the DBI of event loop programming
3 3
4 EV, Event, Glib, Tk, Perl, Event::Lib, Qt, POE - various supported event 4 EV, Event, Glib, Tk, Perl, Event::Lib, Irssi, rxvt-unicode, IO::Async,
5 loops 5 Qt, FLTK and POE are various supported event loops/environments.
6 6
7SYNOPSIS 7SYNOPSIS
8 use AnyEvent; 8 use AnyEvent;
9 9
10 # if you prefer function calls, look at the AE manpage for
11 # an alternative API.
12
13 # file handle or descriptor readable
10 my $w = AnyEvent->io (fh => $fh, poll => "r|w", cb => sub { 14 my $w = AnyEvent->io (fh => $fh, poll => "r", cb => sub { ... });
15
16 # one-shot or repeating timers
17 my $w = AnyEvent->timer (after => $seconds, cb => sub { ... });
18 my $w = AnyEvent->timer (after => $seconds, interval => $seconds, cb => ...);
19
20 print AnyEvent->now; # prints current event loop time
21 print AnyEvent->time; # think Time::HiRes::time or simply CORE::time.
22
23 # POSIX signal
24 my $w = AnyEvent->signal (signal => "TERM", cb => sub { ... });
25
26 # child process exit
27 my $w = AnyEvent->child (pid => $pid, cb => sub {
28 my ($pid, $status) = @_;
11 ... 29 ...
12 }); 30 });
13 31
14 my $w = AnyEvent->timer (after => $seconds, cb => sub { 32 # called when event loop idle (if applicable)
15 ... 33 my $w = AnyEvent->idle (cb => sub { ... });
16 });
17 34
18 my $w = AnyEvent->condvar; # stores whether a condition was flagged 35 my $w = AnyEvent->condvar; # stores whether a condition was flagged
19 $w->send; # wake up current and all future recv's 36 $w->send; # wake up current and all future recv's
20 $w->recv; # enters "main loop" till $condvar gets ->send 37 $w->recv; # enters "main loop" till $condvar gets ->send
38 # use a condvar in callback mode:
39 $w->cb (sub { $_[0]->recv });
40
41INTRODUCTION/TUTORIAL
42 This manpage is mainly a reference manual. If you are interested in a
43 tutorial or some gentle introduction, have a look at the AnyEvent::Intro
44 manpage.
45
46SUPPORT
47 An FAQ document is available as AnyEvent::FAQ.
48
49 There also is a mailinglist for discussing all things AnyEvent, and an
50 IRC channel, too.
51
52 See the AnyEvent project page at the Schmorpforge Ta-Sa Software
53 Repository, at <http://anyevent.schmorp.de>, for more info.
21 54
22WHY YOU SHOULD USE THIS MODULE (OR NOT) 55WHY YOU SHOULD USE THIS MODULE (OR NOT)
23 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen 56 Glib, POE, IO::Async, Event... CPAN offers event models by the dozen
24 nowadays. So what is different about AnyEvent? 57 nowadays. So what is different about AnyEvent?
25 58
26 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of 59 Executive Summary: AnyEvent is *compatible*, AnyEvent is *free of
27 policy* and AnyEvent is *small and efficient*. 60 policy* and AnyEvent is *small and efficient*.
28 61
29 First and foremost, *AnyEvent is not an event model* itself, it only 62 First and foremost, *AnyEvent is not an event model* itself, it only
30 interfaces to whatever event model the main program happens to use in a 63 interfaces to whatever event model the main program happens to use, in a
31 pragmatic way. For event models and certain classes of immortals alike, 64 pragmatic way. For event models and certain classes of immortals alike,
32 the statement "there can only be one" is a bitter reality: In general, 65 the statement "there can only be one" is a bitter reality: In general,
33 only one event loop can be active at the same time in a process. 66 only one event loop can be active at the same time in a process.
34 AnyEvent helps hiding the differences between those event loops. 67 AnyEvent cannot change this, but it can hide the differences between
68 those event loops.
35 69
36 The goal of AnyEvent is to offer module authors the ability to do event 70 The goal of AnyEvent is to offer module authors the ability to do event
37 programming (waiting for I/O or timer events) without subscribing to a 71 programming (waiting for I/O or timer events) without subscribing to a
38 religion, a way of living, and most importantly: without forcing your 72 religion, a way of living, and most importantly: without forcing your
39 module users into the same thing by forcing them to use the same event 73 module users into the same thing by forcing them to use the same event
40 model you use. 74 model you use.
41 75
42 For modules like POE or IO::Async (which is a total misnomer as it is 76 For modules like POE or IO::Async (which is a total misnomer as it is
43 actually doing all I/O *synchronously*...), using them in your module is 77 actually doing all I/O *synchronously*...), using them in your module is
44 like joining a cult: After you joined, you are dependent on them and you 78 like joining a cult: After you join, you are dependent on them and you
45 cannot use anything else, as it is simply incompatible to everything 79 cannot use anything else, as they are simply incompatible to everything
46 that isn't itself. What's worse, all the potential users of your module 80 that isn't them. What's worse, all the potential users of your module
47 are *also* forced to use the same event loop you use. 81 are *also* forced to use the same event loop you use.
48 82
49 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works 83 AnyEvent is different: AnyEvent + POE works fine. AnyEvent + Glib works
50 fine. AnyEvent + Tk works fine etc. etc. but none of these work together 84 fine. AnyEvent + Tk works fine etc. etc. but none of these work together
51 with the rest: POE + IO::Async? No go. Tk + Event? No go. Again: if your 85 with the rest: POE + EV? No go. Tk + Event? No go. Again: if your module
52 module uses one of those, every user of your module has to use it, too. 86 uses one of those, every user of your module has to use it, too. But if
53 But if your module uses AnyEvent, it works transparently with all event 87 your module uses AnyEvent, it works transparently with all event models
54 models it supports (including stuff like POE and IO::Async, as long as 88 it supports (including stuff like IO::Async, as long as those use one of
55 those use one of the supported event loops. It is trivial to add new 89 the supported event loops. It is easy to add new event loops to
56 event loops to AnyEvent, too, so it is future-proof). 90 AnyEvent, too, so it is future-proof).
57 91
58 In addition to being free of having to use *the one and only true event 92 In addition to being free of having to use *the one and only true event
59 model*, AnyEvent also is free of bloat and policy: with POE or similar 93 model*, AnyEvent also is free of bloat and policy: with POE or similar
60 modules, you get an enormous amount of code and strict rules you have to 94 modules, you get an enormous amount of code and strict rules you have to
61 follow. AnyEvent, on the other hand, is lean and up to the point, by 95 follow. AnyEvent, on the other hand, is lean and to the point, by only
62 only offering the functionality that is necessary, in as thin as a 96 offering the functionality that is necessary, in as thin as a wrapper as
63 wrapper as technically possible. 97 technically possible.
64 98
65 Of course, AnyEvent comes with a big (and fully optional!) toolbox of 99 Of course, AnyEvent comes with a big (and fully optional!) toolbox of
66 useful functionality, such as an asynchronous DNS resolver, 100% 100 useful functionality, such as an asynchronous DNS resolver, 100%
67 non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms 101 non-blocking connects (even with TLS/SSL, IPv6 and on broken platforms
68 such as Windows) and lots of real-world knowledge and workarounds for 102 such as Windows) and lots of real-world knowledge and workarounds for
… …
71 Now, if you *do want* lots of policy (this can arguably be somewhat 105 Now, if you *do want* lots of policy (this can arguably be somewhat
72 useful) and you want to force your users to use the one and only event 106 useful) and you want to force your users to use the one and only event
73 model, you should *not* use this module. 107 model, you should *not* use this module.
74 108
75DESCRIPTION 109DESCRIPTION
76 AnyEvent provides an identical interface to multiple event loops. This 110 AnyEvent provides a uniform interface to various event loops. This
77 allows module authors to utilise an event loop without forcing module 111 allows module authors to use event loop functionality without forcing
78 users to use the same event loop (as only a single event loop can 112 module users to use a specific event loop implementation (since more
79 coexist peacefully at any one time). 113 than one event loop cannot coexist peacefully).
80 114
81 The interface itself is vaguely similar, but not identical to the Event 115 The interface itself is vaguely similar, but not identical to the Event
82 module. 116 module.
83 117
84 During the first call of any watcher-creation method, the module tries 118 During the first call of any watcher-creation method, the module tries
85 to detect the currently loaded event loop by probing whether one of the 119 to detect the currently loaded event loop by probing whether one of the
86 following modules is already loaded: EV, Event, Glib, 120 following modules is already loaded: EV, AnyEvent::Loop, Event, Glib,
87 AnyEvent::Impl::Perl, Tk, Event::Lib, Qt, POE. The first one found is 121 Tk, Event::Lib, Qt, POE. The first one found is used. If none are
88 used. If none are found, the module tries to load these modules 122 detected, the module tries to load the first four modules in the order
89 (excluding Tk, Event::Lib, Qt and POE as the pure perl adaptor should 123 given; but note that if EV is not available, the pure-perl
90 always succeed) in the order given. The first one that can be 124 AnyEvent::Loop should always work, so the other two are not normally
91 successfully loaded will be used. If, after this, still none could be 125 tried.
92 found, AnyEvent will fall back to a pure-perl event loop, which is not
93 very efficient, but should work everywhere.
94 126
95 Because AnyEvent first checks for modules that are already loaded, 127 Because AnyEvent first checks for modules that are already loaded,
96 loading an event model explicitly before first using AnyEvent will 128 loading an event model explicitly before first using AnyEvent will
97 likely make that model the default. For example: 129 likely make that model the default. For example:
98 130
… …
100 use AnyEvent; 132 use AnyEvent;
101 133
102 # .. AnyEvent will likely default to Tk 134 # .. AnyEvent will likely default to Tk
103 135
104 The *likely* means that, if any module loads another event model and 136 The *likely* means that, if any module loads another event model and
105 starts using it, all bets are off. Maybe you should tell their authors 137 starts using it, all bets are off - this case should be very rare
106 to use AnyEvent so their modules work together with others seamlessly... 138 though, as very few modules hardcode event loops without announcing this
139 very loudly.
107 140
108 The pure-perl implementation of AnyEvent is called 141 The pure-perl implementation of AnyEvent is called "AnyEvent::Loop".
109 "AnyEvent::Impl::Perl". Like other event modules you can load it 142 Like other event modules you can load it explicitly and enjoy the high
110 explicitly and enjoy the high availability of that event loop :) 143 availability of that event loop :)
111 144
112WATCHERS 145WATCHERS
113 AnyEvent has the central concept of a *watcher*, which is an object that 146 AnyEvent has the central concept of a *watcher*, which is an object that
114 stores relevant data for each kind of event you are waiting for, such as 147 stores relevant data for each kind of event you are waiting for, such as
115 the callback to call, the file handle to watch, etc. 148 the callback to call, the file handle to watch, etc.
… …
117 These watchers are normal Perl objects with normal Perl lifetime. After 150 These watchers are normal Perl objects with normal Perl lifetime. After
118 creating a watcher it will immediately "watch" for events and invoke the 151 creating a watcher it will immediately "watch" for events and invoke the
119 callback when the event occurs (of course, only when the event model is 152 callback when the event occurs (of course, only when the event model is
120 in control). 153 in control).
121 154
155 Note that callbacks must not permanently change global variables
156 potentially in use by the event loop (such as $_ or $[) and that
157 callbacks must not "die". The former is good programming practice in
158 Perl and the latter stems from the fact that exception handling differs
159 widely between event loops.
160
122 To disable the watcher you have to destroy it (e.g. by setting the 161 To disable a watcher you have to destroy it (e.g. by setting the
123 variable you store it in to "undef" or otherwise deleting all references 162 variable you store it in to "undef" or otherwise deleting all references
124 to it). 163 to it).
125 164
126 All watchers are created by calling a method on the "AnyEvent" class. 165 All watchers are created by calling a method on the "AnyEvent" class.
127 166
128 Many watchers either are used with "recursion" (repeating timers for 167 Many watchers either are used with "recursion" (repeating timers for
129 example), or need to refer to their watcher object in other ways. 168 example), or need to refer to their watcher object in other ways.
130 169
131 An any way to achieve that is this pattern: 170 One way to achieve that is this pattern:
132 171
133 my $w; $w = AnyEvent->type (arg => value ..., cb => sub { 172 my $w; $w = AnyEvent->type (arg => value ..., cb => sub {
134 # you can use $w here, for example to undef it 173 # you can use $w here, for example to undef it
135 undef $w; 174 undef $w;
136 }); 175 });
137 176
138 Note that "my $w; $w =" combination. This is necessary because in Perl, 177 Note that "my $w; $w =" combination. This is necessary because in Perl,
139 my variables are only visible after the statement in which they are 178 my variables are only visible after the statement in which they are
140 declared. 179 declared.
141 180
142 I/O WATCHERS 181 I/O WATCHERS
182 $w = AnyEvent->io (
183 fh => <filehandle_or_fileno>,
184 poll => <"r" or "w">,
185 cb => <callback>,
186 );
187
143 You can create an I/O watcher by calling the "AnyEvent->io" method with 188 You can create an I/O watcher by calling the "AnyEvent->io" method with
144 the following mandatory key-value pairs as arguments: 189 the following mandatory key-value pairs as arguments:
145 190
146 "fh" the Perl *file handle* (*not* file descriptor) to watch for events. 191 "fh" is the Perl *file handle* (or a naked file descriptor) to watch for
192 events (AnyEvent might or might not keep a reference to this file
193 handle). Note that only file handles pointing to things for which
194 non-blocking operation makes sense are allowed. This includes sockets,
195 most character devices, pipes, fifos and so on, but not for example
196 files or block devices.
197
147 "poll" must be a string that is either "r" or "w", which creates a 198 "poll" must be a string that is either "r" or "w", which creates a
148 watcher waiting for "r"eadable or "w"ritable events, respectively. "cb" 199 watcher waiting for "r"eadable or "w"ritable events, respectively.
200
149 is the callback to invoke each time the file handle becomes ready. 201 "cb" is the callback to invoke each time the file handle becomes ready.
150 202
151 Although the callback might get passed parameters, their value and 203 Although the callback might get passed parameters, their value and
152 presence is undefined and you cannot rely on them. Portable AnyEvent 204 presence is undefined and you cannot rely on them. Portable AnyEvent
153 callbacks cannot use arguments passed to I/O watcher callbacks. 205 callbacks cannot use arguments passed to I/O watcher callbacks.
154 206
155 The I/O watcher might use the underlying file descriptor or a copy of 207 The I/O watcher might use the underlying file descriptor or a copy of
156 it. You must not close a file handle as long as any watcher is active on 208 it. You must not close a file handle as long as any watcher is active on
157 the underlying file descriptor. 209 the underlying file descriptor.
158 210
159 Some event loops issue spurious readyness notifications, so you should 211 Some event loops issue spurious readiness notifications, so you should
160 always use non-blocking calls when reading/writing from/to your file 212 always use non-blocking calls when reading/writing from/to your file
161 handles. 213 handles.
162 214
163 Example:
164
165 # wait for readability of STDIN, then read a line and disable the watcher 215 Example: wait for readability of STDIN, then read a line and disable the
216 watcher.
217
166 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub { 218 my $w; $w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
167 chomp (my $input = <STDIN>); 219 chomp (my $input = <STDIN>);
168 warn "read: $input\n"; 220 warn "read: $input\n";
169 undef $w; 221 undef $w;
170 }); 222 });
171 223
172 TIME WATCHERS 224 TIME WATCHERS
225 $w = AnyEvent->timer (after => <seconds>, cb => <callback>);
226
227 $w = AnyEvent->timer (
228 after => <fractional_seconds>,
229 interval => <fractional_seconds>,
230 cb => <callback>,
231 );
232
173 You can create a time watcher by calling the "AnyEvent->timer" method 233 You can create a time watcher by calling the "AnyEvent->timer" method
174 with the following mandatory arguments: 234 with the following mandatory arguments:
175 235
176 "after" specifies after how many seconds (fractional values are 236 "after" specifies after how many seconds (fractional values are
177 supported) the callback should be invoked. "cb" is the callback to 237 supported) the callback should be invoked. "cb" is the callback to
… …
179 239
180 Although the callback might get passed parameters, their value and 240 Although the callback might get passed parameters, their value and
181 presence is undefined and you cannot rely on them. Portable AnyEvent 241 presence is undefined and you cannot rely on them. Portable AnyEvent
182 callbacks cannot use arguments passed to time watcher callbacks. 242 callbacks cannot use arguments passed to time watcher callbacks.
183 243
184 The timer callback will be invoked at most once: if you want a repeating 244 The callback will normally be invoked only once. If you specify another
185 timer you have to create a new watcher (this is a limitation by both Tk 245 parameter, "interval", as a strictly positive number (> 0), then the
186 and Glib). 246 callback will be invoked regularly at that interval (in fractional
247 seconds) after the first invocation. If "interval" is specified with a
248 false value, then it is treated as if it were not specified at all.
187 249
188 Example: 250 The callback will be rescheduled before invoking the callback, but no
251 attempt is made to avoid timer drift in most backends, so the interval
252 is only approximate.
189 253
190 # fire an event after 7.7 seconds 254 Example: fire an event after 7.7 seconds.
255
191 my $w = AnyEvent->timer (after => 7.7, cb => sub { 256 my $w = AnyEvent->timer (after => 7.7, cb => sub {
192 warn "timeout\n"; 257 warn "timeout\n";
193 }); 258 });
194 259
195 # to cancel the timer: 260 # to cancel the timer:
196 undef $w; 261 undef $w;
197 262
198 Example 2:
199
200 # fire an event after 0.5 seconds, then roughly every second 263 Example 2: fire an event after 0.5 seconds, then roughly every second.
201 my $w;
202 264
203 my $cb = sub {
204 # cancel the old timer while creating a new one
205 $w = AnyEvent->timer (after => 1, cb => $cb); 265 my $w = AnyEvent->timer (after => 0.5, interval => 1, cb => sub {
266 warn "timeout\n";
206 }; 267 });
207
208 # start the "loop" by creating the first watcher
209 $w = AnyEvent->timer (after => 0.5, cb => $cb);
210 268
211 TIMING ISSUES 269 TIMING ISSUES
212 There are two ways to handle timers: based on real time (relative, "fire 270 There are two ways to handle timers: based on real time (relative, "fire
213 in 10 seconds") and based on wallclock time (absolute, "fire at 12 271 in 10 seconds") and based on wallclock time (absolute, "fire at 12
214 o'clock"). 272 o'clock").
215 273
216 While most event loops expect timers to specified in a relative way, 274 While most event loops expect timers to specified in a relative way,
217 they use absolute time internally. This makes a difference when your 275 they use absolute time internally. This makes a difference when your
218 clock "jumps", for example, when ntp decides to set your clock backwards 276 clock "jumps", for example, when ntp decides to set your clock backwards
219 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is 277 from the wrong date of 2014-01-01 to 2008-01-01, a watcher that is
220 supposed to fire "after" a second might actually take six years to 278 supposed to fire "after a second" might actually take six years to
221 finally fire. 279 finally fire.
222 280
223 AnyEvent cannot compensate for this. The only event loop that is 281 AnyEvent cannot compensate for this. The only event loop that is
224 conscious about these issues is EV, which offers both relative 282 conscious of these issues is EV, which offers both relative (ev_timer,
225 (ev_timer, based on true relative time) and absolute (ev_periodic, based 283 based on true relative time) and absolute (ev_periodic, based on
226 on wallclock time) timers. 284 wallclock time) timers.
227 285
228 AnyEvent always prefers relative timers, if available, matching the 286 AnyEvent always prefers relative timers, if available, matching the
229 AnyEvent API. 287 AnyEvent API.
230 288
231 AnyEvent has two additional methods that return the "current time": 289 AnyEvent has two additional methods that return the "current time":
… …
250 *In almost all cases (in all cases if you don't care), this is the 308 *In almost all cases (in all cases if you don't care), this is the
251 function to call when you want to know the current time.* 309 function to call when you want to know the current time.*
252 310
253 This function is also often faster then "AnyEvent->time", and thus 311 This function is also often faster then "AnyEvent->time", and thus
254 the preferred method if you want some timestamp (for example, 312 the preferred method if you want some timestamp (for example,
255 AnyEvent::Handle uses this to update it's activity timeouts). 313 AnyEvent::Handle uses this to update its activity timeouts).
256 314
257 The rest of this section is only of relevance if you try to be very 315 The rest of this section is only of relevance if you try to be very
258 exact with your timing, you can skip it without bad conscience. 316 exact with your timing; you can skip it without a bad conscience.
259 317
260 For a practical example of when these times differ, consider 318 For a practical example of when these times differ, consider
261 Event::Lib and EV and the following set-up: 319 Event::Lib and EV and the following set-up:
262 320
263 The event loop is running and has just invoked one of your callback 321 The event loop is running and has just invoked one of your callbacks
264 at time=500 (assume no other callbacks delay processing). In your 322 at time=500 (assume no other callbacks delay processing). In your
265 callback, you wait a second by executing "sleep 1" (blocking the 323 callback, you wait a second by executing "sleep 1" (blocking the
266 process for a second) and then (at time=501) you create a relative 324 process for a second) and then (at time=501) you create a relative
267 timer that fires after three seconds. 325 timer that fires after three seconds.
268 326
… …
288 In either case, if you care (and in most cases, you don't), then you 346 In either case, if you care (and in most cases, you don't), then you
289 can get whatever behaviour you want with any event loop, by taking 347 can get whatever behaviour you want with any event loop, by taking
290 the difference between "AnyEvent->time" and "AnyEvent->now" into 348 the difference between "AnyEvent->time" and "AnyEvent->now" into
291 account. 349 account.
292 350
351 AnyEvent->now_update
352 Some event loops (such as EV or AnyEvent::Loop) cache the current
353 time for each loop iteration (see the discussion of AnyEvent->now,
354 above).
355
356 When a callback runs for a long time (or when the process sleeps),
357 then this "current" time will differ substantially from the real
358 time, which might affect timers and time-outs.
359
360 When this is the case, you can call this method, which will update
361 the event loop's idea of "current time".
362
363 A typical example would be a script in a web server (e.g.
364 "mod_perl") - when mod_perl executes the script, then the event loop
365 will have the wrong idea about the "current time" (being potentially
366 far in the past, when the script ran the last time). In that case
367 you should arrange a call to "AnyEvent->now_update" each time the
368 web server process wakes up again (e.g. at the start of your script,
369 or in a handler).
370
371 Note that updating the time *might* cause some events to be handled.
372
293 SIGNAL WATCHERS 373 SIGNAL WATCHERS
374 $w = AnyEvent->signal (signal => <uppercase_signal_name>, cb => <callback>);
375
294 You can watch for signals using a signal watcher, "signal" is the signal 376 You can watch for signals using a signal watcher, "signal" is the signal
295 *name* without any "SIG" prefix, "cb" is the Perl callback to be invoked 377 *name* in uppercase and without any "SIG" prefix, "cb" is the Perl
296 whenever a signal occurs. 378 callback to be invoked whenever a signal occurs.
297 379
298 Although the callback might get passed parameters, their value and 380 Although the callback might get passed parameters, their value and
299 presence is undefined and you cannot rely on them. Portable AnyEvent 381 presence is undefined and you cannot rely on them. Portable AnyEvent
300 callbacks cannot use arguments passed to signal watcher callbacks. 382 callbacks cannot use arguments passed to signal watcher callbacks.
301 383
… …
303 invocation, and callback invocation will be synchronous. Synchronous 385 invocation, and callback invocation will be synchronous. Synchronous
304 means that it might take a while until the signal gets handled by the 386 means that it might take a while until the signal gets handled by the
305 process, but it is guaranteed not to interrupt any other callbacks. 387 process, but it is guaranteed not to interrupt any other callbacks.
306 388
307 The main advantage of using these watchers is that you can share a 389 The main advantage of using these watchers is that you can share a
308 signal between multiple watchers. 390 signal between multiple watchers, and AnyEvent will ensure that signals
391 will not interrupt your program at bad times.
309 392
310 This watcher might use %SIG, so programs overwriting those signals 393 This watcher might use %SIG (depending on the event loop used), so
311 directly will likely not work correctly. 394 programs overwriting those signals directly will likely not work
395 correctly.
312 396
313 Example: exit on SIGINT 397 Example: exit on SIGINT
314 398
315 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 }); 399 my $w = AnyEvent->signal (signal => "INT", cb => sub { exit 1 });
316 400
401 Restart Behaviour
402 While restart behaviour is up to the event loop implementation, most
403 will not restart syscalls (that includes Async::Interrupt and AnyEvent's
404 pure perl implementation).
405
406 Safe/Unsafe Signals
407 Perl signals can be either "safe" (synchronous to opcode handling) or
408 "unsafe" (asynchronous) - the former might delay signal delivery
409 indefinitely, the latter might corrupt your memory.
410
411 AnyEvent signal handlers are, in addition, synchronous to the event
412 loop, i.e. they will not interrupt your running perl program but will
413 only be called as part of the normal event handling (just like timer,
414 I/O etc. callbacks, too).
415
416 Signal Races, Delays and Workarounds
417 Many event loops (e.g. Glib, Tk, Qt, IO::Async) do not support attaching
418 callbacks to signals in a generic way, which is a pity, as you cannot do
419 race-free signal handling in perl, requiring C libraries for this.
420 AnyEvent will try to do its best, which means in some cases, signals
421 will be delayed. The maximum time a signal might be delayed is 10
422 seconds by default, but can be overriden via
423 $ENV{PERL_ANYEVENT_MAX_SIGNAL_LATENCY} or $AnyEvent::MAX_SIGNAL_LATENCY
424 - see the "ENVIRONMENT VARIABLES" section for details.
425
426 All these problems can be avoided by installing the optional
427 Async::Interrupt module, which works with most event loops. It will not
428 work with inherently broken event loops such as Event or Event::Lib (and
429 not with POE currently). For those, you just have to suffer the delays.
430
317 CHILD PROCESS WATCHERS 431 CHILD PROCESS WATCHERS
432 $w = AnyEvent->child (pid => <process id>, cb => <callback>);
433
318 You can also watch on a child process exit and catch its exit status. 434 You can also watch for a child process exit and catch its exit status.
319 435
320 The child process is specified by the "pid" argument (if set to 0, it 436 The child process is specified by the "pid" argument (on some backends,
321 watches for any child process exit). The watcher will trigger as often 437 using 0 watches for any child process exit, on others this will croak).
322 as status change for the child are received. This works by installing a 438 The watcher will be triggered only when the child process has finished
323 signal handler for "SIGCHLD". The callback will be called with the pid 439 and an exit status is available, not on any trace events
324 and exit status (as returned by waitpid), so unlike other watcher types, 440 (stopped/continued).
325 you *can* rely on child watcher callback arguments. 441
442 The callback will be called with the pid and exit status (as returned by
443 waitpid), so unlike other watcher types, you *can* rely on child watcher
444 callback arguments.
445
446 This watcher type works by installing a signal handler for "SIGCHLD",
447 and since it cannot be shared, nothing else should use SIGCHLD or reap
448 random child processes (waiting for specific child processes, e.g.
449 inside "system", is just fine).
326 450
327 There is a slight catch to child watchers, however: you usually start 451 There is a slight catch to child watchers, however: you usually start
328 them *after* the child process was created, and this means the process 452 them *after* the child process was created, and this means the process
329 could have exited already (and no SIGCHLD will be sent anymore). 453 could have exited already (and no SIGCHLD will be sent anymore).
330 454
331 Not all event models handle this correctly (POE doesn't), but even for 455 Not all event models handle this correctly (neither POE nor IO::Async
456 do, see their AnyEvent::Impl manpages for details), but even for event
332 event models that *do* handle this correctly, they usually need to be 457 models that *do* handle this correctly, they usually need to be loaded
333 loaded before the process exits (i.e. before you fork in the first 458 before the process exits (i.e. before you fork in the first place).
334 place). 459 AnyEvent's pure perl event loop handles all cases correctly regardless
460 of when you start the watcher.
335 461
336 This means you cannot create a child watcher as the very first thing in 462 This means you cannot create a child watcher as the very first thing in
337 an AnyEvent program, you *have* to create at least one watcher before 463 an AnyEvent program, you *have* to create at least one watcher before
338 you "fork" the child (alternatively, you can call "AnyEvent::detect"). 464 you "fork" the child (alternatively, you can call "AnyEvent::detect").
339 465
466 As most event loops do not support waiting for child events, they will
467 be emulated by AnyEvent in most cases, in which case the latency and
468 race problems mentioned in the description of signal watchers apply.
469
340 Example: fork a process and wait for it 470 Example: fork a process and wait for it
341 471
342 my $done = AnyEvent->condvar; 472 my $done = AnyEvent->condvar;
343 473
344 my $pid = fork or exit 5; 474 my $pid = fork or exit 5;
345 475
346 my $w = AnyEvent->child ( 476 my $w = AnyEvent->child (
347 pid => $pid, 477 pid => $pid,
348 cb => sub { 478 cb => sub {
349 my ($pid, $status) = @_; 479 my ($pid, $status) = @_;
350 warn "pid $pid exited with status $status"; 480 warn "pid $pid exited with status $status";
351 $done->send; 481 $done->send;
352 }, 482 },
353 ); 483 );
354 484
355 # do something else, then wait for process exit 485 # do something else, then wait for process exit
356 $done->recv; 486 $done->recv;
487
488 IDLE WATCHERS
489 $w = AnyEvent->idle (cb => <callback>);
490
491 This will repeatedly invoke the callback after the process becomes idle,
492 until either the watcher is destroyed or new events have been detected.
493
494 Idle watchers are useful when there is a need to do something, but it is
495 not so important (or wise) to do it instantly. The callback will be
496 invoked only when there is "nothing better to do", which is usually
497 defined as "all outstanding events have been handled and no new events
498 have been detected". That means that idle watchers ideally get invoked
499 when the event loop has just polled for new events but none have been
500 detected. Instead of blocking to wait for more events, the idle watchers
501 will be invoked.
502
503 Unfortunately, most event loops do not really support idle watchers
504 (only EV, Event and Glib do it in a usable fashion) - for the rest,
505 AnyEvent will simply call the callback "from time to time".
506
507 Example: read lines from STDIN, but only process them when the program
508 is otherwise idle:
509
510 my @lines; # read data
511 my $idle_w;
512 my $io_w = AnyEvent->io (fh => \*STDIN, poll => 'r', cb => sub {
513 push @lines, scalar <STDIN>;
514
515 # start an idle watcher, if not already done
516 $idle_w ||= AnyEvent->idle (cb => sub {
517 # handle only one line, when there are lines left
518 if (my $line = shift @lines) {
519 print "handled when idle: $line";
520 } else {
521 # otherwise disable the idle watcher again
522 undef $idle_w;
523 }
524 });
525 });
357 526
358 CONDITION VARIABLES 527 CONDITION VARIABLES
528 $cv = AnyEvent->condvar;
529
530 $cv->send (<list>);
531 my @res = $cv->recv;
532
359 If you are familiar with some event loops you will know that all of them 533 If you are familiar with some event loops you will know that all of them
360 require you to run some blocking "loop", "run" or similar function that 534 require you to run some blocking "loop", "run" or similar function that
361 will actively watch for new events and call your callbacks. 535 will actively watch for new events and call your callbacks.
362 536
363 AnyEvent is different, it expects somebody else to run the event loop 537 AnyEvent is slightly different: it expects somebody else to run the
364 and will only block when necessary (usually when told by the user). 538 event loop and will only block when necessary (usually when told by the
539 user).
365 540
366 The instrument to do that is called a "condition variable", so called 541 The tool to do that is called a "condition variable", so called because
367 because they represent a condition that must become true. 542 they represent a condition that must become true.
543
544 Now is probably a good time to look at the examples further below.
368 545
369 Condition variables can be created by calling the "AnyEvent->condvar" 546 Condition variables can be created by calling the "AnyEvent->condvar"
370 method, usually without arguments. The only argument pair allowed is 547 method, usually without arguments. The only argument pair allowed is
371 "cb", which specifies a callback to be called when the condition 548 "cb", which specifies a callback to be called when the condition
372 variable becomes true. 549 variable becomes true, with the condition variable as the first argument
550 (but not the results).
373 551
374 After creation, the condition variable is "false" until it becomes 552 After creation, the condition variable is "false" until it becomes
375 "true" by calling the "send" method (or calling the condition variable 553 "true" by calling the "send" method (or calling the condition variable
376 as if it were a callback, read about the caveats in the description for 554 as if it were a callback, read about the caveats in the description for
377 the "->send" method). 555 the "->send" method).
378 556
379 Condition variables are similar to callbacks, except that you can 557 Since condition variables are the most complex part of the AnyEvent API,
380 optionally wait for them. They can also be called merge points - points 558 here are some different mental models of what they are - pick the ones
381 in time where multiple outstanding events have been processed. And yet 559 you can connect to:
382 another way to call them is transactions - each condition variable can 560
383 be used to represent a transaction, which finishes at some point and 561 * Condition variables are like callbacks - you can call them (and pass
384 delivers a result. 562 them instead of callbacks). Unlike callbacks however, you can also
563 wait for them to be called.
564
565 * Condition variables are signals - one side can emit or send them,
566 the other side can wait for them, or install a handler that is
567 called when the signal fires.
568
569 * Condition variables are like "Merge Points" - points in your program
570 where you merge multiple independent results/control flows into one.
571
572 * Condition variables represent a transaction - functions that start
573 some kind of transaction can return them, leaving the caller the
574 choice between waiting in a blocking fashion, or setting a callback.
575
576 * Condition variables represent future values, or promises to deliver
577 some result, long before the result is available.
385 578
386 Condition variables are very useful to signal that something has 579 Condition variables are very useful to signal that something has
387 finished, for example, if you write a module that does asynchronous http 580 finished, for example, if you write a module that does asynchronous http
388 requests, then a condition variable would be the ideal candidate to 581 requests, then a condition variable would be the ideal candidate to
389 signal the availability of results. The user can either act when the 582 signal the availability of results. The user can either act when the
… …
402 595
403 Condition variables are represented by hash refs in perl, and the keys 596 Condition variables are represented by hash refs in perl, and the keys
404 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy 597 used by AnyEvent itself are all named "_ae_XXX" to make subclassing easy
405 (it is often useful to build your own transaction class on top of 598 (it is often useful to build your own transaction class on top of
406 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call 599 AnyEvent). To subclass, use "AnyEvent::CondVar" as base class and call
407 it's "new" method in your own "new" method. 600 its "new" method in your own "new" method.
408 601
409 There are two "sides" to a condition variable - the "producer side" 602 There are two "sides" to a condition variable - the "producer side"
410 which eventually calls "-> send", and the "consumer side", which waits 603 which eventually calls "-> send", and the "consumer side", which waits
411 for the send to occur. 604 for the send to occur.
412 605
413 Example: wait for a timer. 606 Example: wait for a timer.
414 607
415 # wait till the result is ready 608 # condition: "wait till the timer is fired"
416 my $result_ready = AnyEvent->condvar; 609 my $timer_fired = AnyEvent->condvar;
417 610
418 # do something such as adding a timer 611 # create the timer - we could wait for, say
419 # or socket watcher the calls $result_ready->send 612 # a handle becomign ready, or even an
420 # when the "result" is ready. 613 # AnyEvent::HTTP request to finish, but
421 # in this case, we simply use a timer: 614 # in this case, we simply use a timer:
422 my $w = AnyEvent->timer ( 615 my $w = AnyEvent->timer (
423 after => 1, 616 after => 1,
424 cb => sub { $result_ready->send }, 617 cb => sub { $timer_fired->send },
425 ); 618 );
426 619
427 # this "blocks" (while handling events) till the callback 620 # this "blocks" (while handling events) till the callback
428 # calls send 621 # calls ->send
429 $result_ready->recv; 622 $timer_fired->recv;
430 623
431 Example: wait for a timer, but take advantage of the fact that condition 624 Example: wait for a timer, but take advantage of the fact that condition
432 variables are also code references. 625 variables are also callable directly.
433 626
434 my $done = AnyEvent->condvar; 627 my $done = AnyEvent->condvar;
435 my $delay = AnyEvent->timer (after => 5, cb => $done); 628 my $delay = AnyEvent->timer (after => 5, cb => $done);
436 $done->recv; 629 $done->recv;
630
631 Example: Imagine an API that returns a condvar and doesn't support
632 callbacks. This is how you make a synchronous call, for example from the
633 main program:
634
635 use AnyEvent::CouchDB;
636
637 ...
638
639 my @info = $couchdb->info->recv;
640
641 And this is how you would just set a callback to be called whenever the
642 results are available:
643
644 $couchdb->info->cb (sub {
645 my @info = $_[0]->recv;
646 });
437 647
438 METHODS FOR PRODUCERS 648 METHODS FOR PRODUCERS
439 These methods should only be used by the producing side, i.e. the 649 These methods should only be used by the producing side, i.e. the
440 code/module that eventually sends the signal. Note that it is also the 650 code/module that eventually sends the signal. Note that it is also the
441 producer side which creates the condvar in most cases, but it isn't 651 producer side which creates the condvar in most cases, but it isn't
… …
451 661
452 Any arguments passed to the "send" call will be returned by all 662 Any arguments passed to the "send" call will be returned by all
453 future "->recv" calls. 663 future "->recv" calls.
454 664
455 Condition variables are overloaded so one can call them directly (as 665 Condition variables are overloaded so one can call them directly (as
456 a code reference). Calling them directly is the same as calling 666 if they were a code reference). Calling them directly is the same as
457 "send". Note, however, that many C-based event loops do not handle 667 calling "send".
458 overloading, so as tempting as it may be, passing a condition
459 variable instead of a callback does not work. Both the pure perl and
460 EV loops support overloading, however, as well as all functions that
461 use perl to invoke a callback (as in AnyEvent::Socket and
462 AnyEvent::DNS for example).
463 668
464 $cv->croak ($error) 669 $cv->croak ($error)
465 Similar to send, but causes all call's to "->recv" to invoke 670 Similar to send, but causes all calls to "->recv" to invoke
466 "Carp::croak" with the given error message/object/scalar. 671 "Carp::croak" with the given error message/object/scalar.
467 672
468 This can be used to signal any errors to the condition variable 673 This can be used to signal any errors to the condition variable
469 user/consumer. 674 user/consumer. Doing it this way instead of calling "croak" directly
675 delays the error detection, but has the overwhelming advantage that
676 it diagnoses the error at the place where the result is expected,
677 and not deep in some event callback with no connection to the actual
678 code causing the problem.
470 679
471 $cv->begin ([group callback]) 680 $cv->begin ([group callback])
472 $cv->end 681 $cv->end
473 These two methods are EXPERIMENTAL and MIGHT CHANGE.
474
475 These two methods can be used to combine many transactions/events 682 These two methods can be used to combine many transactions/events
476 into one. For example, a function that pings many hosts in parallel 683 into one. For example, a function that pings many hosts in parallel
477 might want to use a condition variable for the whole process. 684 might want to use a condition variable for the whole process.
478 685
479 Every call to "->begin" will increment a counter, and every call to 686 Every call to "->begin" will increment a counter, and every call to
480 "->end" will decrement it. If the counter reaches 0 in "->end", the 687 "->end" will decrement it. If the counter reaches 0 in "->end", the
481 (last) callback passed to "begin" will be executed. That callback is 688 (last) callback passed to "begin" will be executed, passing the
482 *supposed* to call "->send", but that is not required. If no 689 condvar as first argument. That callback is *supposed* to call
690 "->send", but that is not required. If no group callback was set,
483 callback was set, "send" will be called without any arguments. 691 "send" will be called without any arguments.
484 692
485 Let's clarify this with the ping example: 693 You can think of "$cv->send" giving you an OR condition (one call
694 sends), while "$cv->begin" and "$cv->end" giving you an AND
695 condition (all "begin" calls must be "end"'ed before the condvar
696 sends).
697
698 Let's start with a simple example: you have two I/O watchers (for
699 example, STDOUT and STDERR for a program), and you want to wait for
700 both streams to close before activating a condvar:
486 701
487 my $cv = AnyEvent->condvar; 702 my $cv = AnyEvent->condvar;
488 703
704 $cv->begin; # first watcher
705 my $w1 = AnyEvent->io (fh => $fh1, cb => sub {
706 defined sysread $fh1, my $buf, 4096
707 or $cv->end;
708 });
709
710 $cv->begin; # second watcher
711 my $w2 = AnyEvent->io (fh => $fh2, cb => sub {
712 defined sysread $fh2, my $buf, 4096
713 or $cv->end;
714 });
715
716 $cv->recv;
717
718 This works because for every event source (EOF on file handle),
719 there is one call to "begin", so the condvar waits for all calls to
720 "end" before sending.
721
722 The ping example mentioned above is slightly more complicated, as
723 the there are results to be passwd back, and the number of tasks
724 that are begun can potentially be zero:
725
726 my $cv = AnyEvent->condvar;
727
489 my %result; 728 my %result;
490 $cv->begin (sub { $cv->send (\%result) }); 729 $cv->begin (sub { shift->send (\%result) });
491 730
492 for my $host (@list_of_hosts) { 731 for my $host (@list_of_hosts) {
493 $cv->begin; 732 $cv->begin;
494 ping_host_then_call_callback $host, sub { 733 ping_host_then_call_callback $host, sub {
495 $result{$host} = ...; 734 $result{$host} = ...;
… …
497 }; 736 };
498 } 737 }
499 738
500 $cv->end; 739 $cv->end;
501 740
741 ...
742
743 my $results = $cv->recv;
744
502 This code fragment supposedly pings a number of hosts and calls 745 This code fragment supposedly pings a number of hosts and calls
503 "send" after results for all then have have been gathered - in any 746 "send" after results for all then have have been gathered - in any
504 order. To achieve this, the code issues a call to "begin" when it 747 order. To achieve this, the code issues a call to "begin" when it
505 starts each ping request and calls "end" when it has received some 748 starts each ping request and calls "end" when it has received some
506 result for it. Since "begin" and "end" only maintain a counter, the 749 result for it. Since "begin" and "end" only maintain a counter, the
… …
510 the loop, which serves two important purposes: first, it sets the 753 the loop, which serves two important purposes: first, it sets the
511 callback to be called once the counter reaches 0, and second, it 754 callback to be called once the counter reaches 0, and second, it
512 ensures that "send" is called even when "no" hosts are being pinged 755 ensures that "send" is called even when "no" hosts are being pinged
513 (the loop doesn't execute once). 756 (the loop doesn't execute once).
514 757
515 This is the general pattern when you "fan out" into multiple 758 This is the general pattern when you "fan out" into multiple (but
516 subrequests: use an outer "begin"/"end" pair to set the callback and 759 potentially zero) subrequests: use an outer "begin"/"end" pair to
517 ensure "end" is called at least once, and then, for each subrequest 760 set the callback and ensure "end" is called at least once, and then,
518 you start, call "begin" and for each subrequest you finish, call 761 for each subrequest you start, call "begin" and for each subrequest
519 "end". 762 you finish, call "end".
520 763
521 METHODS FOR CONSUMERS 764 METHODS FOR CONSUMERS
522 These methods should only be used by the consuming side, i.e. the code 765 These methods should only be used by the consuming side, i.e. the code
523 awaits the condition. 766 awaits the condition.
524 767
525 $cv->recv 768 $cv->recv
526 Wait (blocking if necessary) until the "->send" or "->croak" methods 769 Wait (blocking if necessary) until the "->send" or "->croak" methods
527 have been called on c<$cv>, while servicing other watchers normally. 770 have been called on $cv, while servicing other watchers normally.
528 771
529 You can only wait once on a condition - additional calls are valid 772 You can only wait once on a condition - additional calls are valid
530 but will return immediately. 773 but will return immediately.
531 774
532 If an error condition has been set by calling "->croak", then this 775 If an error condition has been set by calling "->croak", then this
533 function will call "croak". 776 function will call "croak".
534 777
535 In list context, all parameters passed to "send" will be returned, 778 In list context, all parameters passed to "send" will be returned,
536 in scalar context only the first one will be returned. 779 in scalar context only the first one will be returned.
537 780
781 Note that doing a blocking wait in a callback is not supported by
782 any event loop, that is, recursive invocation of a blocking "->recv"
783 is not allowed and the "recv" call will "croak" if such a condition
784 is detected. This requirement can be dropped by relying on
785 Coro::AnyEvent , which allows you to do a blocking "->recv" from any
786 thread that doesn't run the event loop itself. Coro::AnyEvent is
787 loaded automatically when Coro is used with AnyEvent, so code does
788 not need to do anything special to take advantage of that: any code
789 that would normally block your program because it calls "recv", be
790 executed in an "async" thread instead without blocking other
791 threads.
792
538 Not all event models support a blocking wait - some die in that case 793 Not all event models support a blocking wait - some die in that case
539 (programs might want to do that to stay interactive), so *if you are 794 (programs might want to do that to stay interactive), so *if you are
540 using this from a module, never require a blocking wait*, but let 795 using this from a module, never require a blocking wait*. Instead,
541 the caller decide whether the call will block or not (for example, 796 let the caller decide whether the call will block or not (for
542 by coupling condition variables with some kind of request results 797 example, by coupling condition variables with some kind of request
543 and supporting callbacks so the caller knows that getting the result 798 results and supporting callbacks so the caller knows that getting
544 will not block, while still supporting blocking waits if the caller 799 the result will not block, while still supporting blocking waits if
545 so desires). 800 the caller so desires).
546 801
547 Another reason *never* to "->recv" in a module is that you cannot
548 sensibly have two "->recv"'s in parallel, as that would require
549 multiple interpreters or coroutines/threads, none of which
550 "AnyEvent" can supply.
551
552 The Coro module, however, *can* and *does* supply coroutines and, in
553 fact, Coro::AnyEvent replaces AnyEvent's condvars by coroutine-safe
554 versions and also integrates coroutines into AnyEvent, making
555 blocking "->recv" calls perfectly safe as long as they are done from
556 another coroutine (one that doesn't run the event loop).
557
558 You can ensure that "-recv" never blocks by setting a callback and 802 You can ensure that "->recv" never blocks by setting a callback and
559 only calling "->recv" from within that callback (or at a later 803 only calling "->recv" from within that callback (or at a later
560 time). This will work even when the event loop does not support 804 time). This will work even when the event loop does not support
561 blocking waits otherwise. 805 blocking waits otherwise.
562 806
563 $bool = $cv->ready 807 $bool = $cv->ready
564 Returns true when the condition is "true", i.e. whether "send" or 808 Returns true when the condition is "true", i.e. whether "send" or
565 "croak" have been called. 809 "croak" have been called.
566 810
567 $cb = $cv->cb ([new callback]) 811 $cb = $cv->cb ($cb->($cv))
568 This is a mutator function that returns the callback set and 812 This is a mutator function that returns the callback set and
569 optionally replaces it before doing so. 813 optionally replaces it before doing so.
570 814
571 The callback will be called when the condition becomes "true", i.e. 815 The callback will be called when the condition becomes "true", i.e.
572 when "send" or "croak" are called. Calling "recv" inside the 816 when "send" or "croak" are called, with the only argument being the
817 condition variable itself. If the condition is already true, the
818 callback is called immediately when it is set. Calling "recv" inside
573 callback or at any later time is guaranteed not to block. 819 the callback or at any later time is guaranteed not to block.
820
821SUPPORTED EVENT LOOPS/BACKENDS
822 The available backend classes are (every class has its own manpage):
823
824 Backends that are autoprobed when no other event loop can be found.
825 EV is the preferred backend when no other event loop seems to be in
826 use. If EV is not installed, then AnyEvent will fall back to its own
827 pure-perl implementation, which is available everywhere as it comes
828 with AnyEvent itself.
829
830 AnyEvent::Impl::EV based on EV (interface to libev, best choice).
831 AnyEvent::Impl::Perl pure-perl AnyEvent::Loop, fast and portable.
832
833 Backends that are transparently being picked up when they are used.
834 These will be used if they are already loaded when the first watcher
835 is created, in which case it is assumed that the application is
836 using them. This means that AnyEvent will automatically pick the
837 right backend when the main program loads an event module before
838 anything starts to create watchers. Nothing special needs to be done
839 by the main program.
840
841 AnyEvent::Impl::Event based on Event, very stable, few glitches.
842 AnyEvent::Impl::Glib based on Glib, slow but very stable.
843 AnyEvent::Impl::Tk based on Tk, very broken.
844 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
845 AnyEvent::Impl::POE based on POE, very slow, some limitations.
846 AnyEvent::Impl::Irssi used when running within irssi.
847 AnyEvent::Impl::IOAsync based on IO::Async.
848 AnyEvent::Impl::Cocoa based on Cocoa::EventLoop.
849 AnyEvent::Impl::FLTK based on FLTK (fltk 2 binding).
850
851 Backends with special needs.
852 Qt requires the Qt::Application to be instantiated first, but will
853 otherwise be picked up automatically. As long as the main program
854 instantiates the application before any AnyEvent watchers are
855 created, everything should just work.
856
857 AnyEvent::Impl::Qt based on Qt.
858
859 Event loops that are indirectly supported via other backends.
860 Some event loops can be supported via other modules:
861
862 There is no direct support for WxWidgets (Wx) or Prima.
863
864 WxWidgets has no support for watching file handles. However, you can
865 use WxWidgets through the POE adaptor, as POE has a Wx backend that
866 simply polls 20 times per second, which was considered to be too
867 horrible to even consider for AnyEvent.
868
869 Prima is not supported as nobody seems to be using it, but it has a
870 POE backend, so it can be supported through POE.
871
872 AnyEvent knows about both Prima and Wx, however, and will try to
873 load POE when detecting them, in the hope that POE will pick them
874 up, in which case everything will be automatic.
574 875
575GLOBAL VARIABLES AND FUNCTIONS 876GLOBAL VARIABLES AND FUNCTIONS
877 These are not normally required to use AnyEvent, but can be useful to
878 write AnyEvent extension modules.
879
576 $AnyEvent::MODEL 880 $AnyEvent::MODEL
577 Contains "undef" until the first watcher is being created. Then it 881 Contains "undef" until the first watcher is being created, before
882 the backend has been autodetected.
883
578 contains the event model that is being used, which is the name of 884 Afterwards it contains the event model that is being used, which is
579 the Perl class implementing the model. This class is usually one of 885 the name of the Perl class implementing the model. This class is
580 the "AnyEvent::Impl:xxx" modules, but can be any other class in the 886 usually one of the "AnyEvent::Impl::xxx" modules, but can be any
581 case AnyEvent has been extended at runtime (e.g. in *rxvt-unicode*). 887 other class in the case AnyEvent has been extended at runtime (e.g.
582 888 in *rxvt-unicode* it will be "urxvt::anyevent").
583 The known classes so far are:
584
585 AnyEvent::Impl::EV based on EV (an interface to libev, best choice).
586 AnyEvent::Impl::Event based on Event, second best choice.
587 AnyEvent::Impl::Perl pure-perl implementation, fast and portable.
588 AnyEvent::Impl::Glib based on Glib, third-best choice.
589 AnyEvent::Impl::Tk based on Tk, very bad choice.
590 AnyEvent::Impl::Qt based on Qt, cannot be autoprobed (see its docs).
591 AnyEvent::Impl::EventLib based on Event::Lib, leaks memory and worse.
592 AnyEvent::Impl::POE based on POE, not generic enough for full support.
593
594 There is no support for WxWidgets, as WxWidgets has no support for
595 watching file handles. However, you can use WxWidgets through the
596 POE Adaptor, as POE has a Wx backend that simply polls 20 times per
597 second, which was considered to be too horrible to even consider for
598 AnyEvent. Likewise, other POE backends can be used by AnyEvent by
599 using it's adaptor.
600
601 AnyEvent knows about Prima and Wx and will try to use POE when
602 autodetecting them.
603 889
604 AnyEvent::detect 890 AnyEvent::detect
605 Returns $AnyEvent::MODEL, forcing autodetection of the event model 891 Returns $AnyEvent::MODEL, forcing autodetection of the event model
606 if necessary. You should only call this function right before you 892 if necessary. You should only call this function right before you
607 would have created an AnyEvent watcher anyway, that is, as late as 893 would have created an AnyEvent watcher anyway, that is, as late as
608 possible at runtime. 894 possible at runtime, and not e.g. during initialisation of your
895 module.
896
897 The effect of calling this function is as if a watcher had been
898 created (specifically, actions that happen "when the first watcher
899 is created" happen when calling detetc as well).
900
901 If you need to do some initialisation before AnyEvent watchers are
902 created, use "post_detect".
609 903
610 $guard = AnyEvent::post_detect { BLOCK } 904 $guard = AnyEvent::post_detect { BLOCK }
611 Arranges for the code block to be executed as soon as the event 905 Arranges for the code block to be executed as soon as the event
612 model is autodetected (or immediately if this has already happened). 906 model is autodetected (or immediately if that has already happened).
907
908 The block will be executed *after* the actual backend has been
909 detected ($AnyEvent::MODEL is set), but *before* any watchers have
910 been created, so it is possible to e.g. patch @AnyEvent::ISA or do
911 other initialisations - see the sources of AnyEvent::Strict or
912 AnyEvent::AIO to see how this is used.
913
914 The most common usage is to create some global watchers, without
915 forcing event module detection too early, for example, AnyEvent::AIO
916 creates and installs the global IO::AIO watcher in a "post_detect"
917 block to avoid autodetecting the event module at load time.
613 918
614 If called in scalar or list context, then it creates and returns an 919 If called in scalar or list context, then it creates and returns an
615 object that automatically removes the callback again when it is 920 object that automatically removes the callback again when it is
921 destroyed (or "undef" when the hook was immediately executed). See
616 destroyed. See Coro::BDB for a case where this is useful. 922 AnyEvent::AIO for a case where this is useful.
923
924 Example: Create a watcher for the IO::AIO module and store it in
925 $WATCHER, but do so only do so after the event loop is initialised.
926
927 our WATCHER;
928
929 my $guard = AnyEvent::post_detect {
930 $WATCHER = AnyEvent->io (fh => IO::AIO::poll_fileno, poll => 'r', cb => \&IO::AIO::poll_cb);
931 };
932
933 # the ||= is important in case post_detect immediately runs the block,
934 # as to not clobber the newly-created watcher. assigning both watcher and
935 # post_detect guard to the same variable has the advantage of users being
936 # able to just C<undef $WATCHER> if the watcher causes them grief.
937
938 $WATCHER ||= $guard;
617 939
618 @AnyEvent::post_detect 940 @AnyEvent::post_detect
619 If there are any code references in this array (you can "push" to it 941 If there are any code references in this array (you can "push" to it
620 before or after loading AnyEvent), then they will called directly 942 before or after loading AnyEvent), then they will be called directly
621 after the event loop has been chosen. 943 after the event loop has been chosen.
622 944
623 You should check $AnyEvent::MODEL before adding to this array, 945 You should check $AnyEvent::MODEL before adding to this array,
624 though: if it contains a true value then the event loop has already 946 though: if it is defined then the event loop has already been
625 been detected, and the array will be ignored. 947 detected, and the array will be ignored.
626 948
627 Best use "AnyEvent::post_detect { BLOCK }" instead. 949 Best use "AnyEvent::post_detect { BLOCK }" when your application
950 allows it, as it takes care of these details.
951
952 This variable is mainly useful for modules that can do something
953 useful when AnyEvent is used and thus want to know when it is
954 initialised, but do not need to even load it by default. This array
955 provides the means to hook into AnyEvent passively, without loading
956 it.
957
958 Example: To load Coro::AnyEvent whenever Coro and AnyEvent are used
959 together, you could put this into Coro (this is the actual code used
960 by Coro to accomplish this):
961
962 if (defined $AnyEvent::MODEL) {
963 # AnyEvent already initialised, so load Coro::AnyEvent
964 require Coro::AnyEvent;
965 } else {
966 # AnyEvent not yet initialised, so make sure to load Coro::AnyEvent
967 # as soon as it is
968 push @AnyEvent::post_detect, sub { require Coro::AnyEvent };
969 }
970
971 AnyEvent::postpone { BLOCK }
972 Arranges for the block to be executed as soon as possible, but not
973 before the call itself returns. In practise, the block will be
974 executed just before the event loop polls for new events, or shortly
975 afterwards.
976
977 This function never returns anything (to make the "return postpone {
978 ... }" idiom more useful.
979
980 To understand the usefulness of this function, consider a function
981 that asynchronously does something for you and returns some
982 transaction object or guard to let you cancel the operation. For
983 example, "AnyEvent::Socket::tcp_connect":
984
985 # start a conenction attempt unless one is active
986 $self->{connect_guard} ||= AnyEvent::Socket::tcp_connect "www.example.net", 80, sub {
987 delete $self->{connect_guard};
988 ...
989 };
990
991 Imagine that this function could instantly call the callback, for
992 example, because it detects an obvious error such as a negative port
993 number. Invoking the callback before the function returns causes
994 problems however: the callback will be called and will try to delete
995 the guard object. But since the function hasn't returned yet, there
996 is nothing to delete. When the function eventually returns it will
997 assign the guard object to "$self->{connect_guard}", where it will
998 likely never be deleted, so the program thinks it is still trying to
999 connect.
1000
1001 This is where "AnyEvent::postpone" should be used. Instead of
1002 calling the callback directly on error:
1003
1004 $cb->(undef), return # signal error to callback, BAD!
1005 if $some_error_condition;
1006
1007 It should use "postpone":
1008
1009 AnyEvent::postpone { $cb->(undef) }, return # signal error to callback, later
1010 if $some_error_condition;
1011
1012 AnyEvent::log $level, $msg[, @args]
1013 Log the given $msg at the given $level.
1014
1015 If AnyEvent::Log is not loaded then this function makes a simple
1016 test to see whether the message will be logged. If the test succeeds
1017 it will load AnyEvent::Log and call "AnyEvent::Log::log" -
1018 consequently, look at the AnyEvent::Log documentation for details.
1019
1020 If the test fails it will simply return. Right now this happens when
1021 a numerical loglevel is used and it is larger than the level
1022 specified via $ENV{PERL_ANYEVENT_VERBOSE}.
1023
1024 If you want to sprinkle loads of logging calls around your code,
1025 consider creating a logger callback with the "AnyEvent::Log::logger"
1026 function, which can reduce typing, codesize and can reduce the
1027 logging overhead enourmously.
628 1028
629WHAT TO DO IN A MODULE 1029WHAT TO DO IN A MODULE
630 As a module author, you should "use AnyEvent" and call AnyEvent methods 1030 As a module author, you should "use AnyEvent" and call AnyEvent methods
631 freely, but you should not load a specific event module or rely on it. 1031 freely, but you should not load a specific event module or rely on it.
632 1032
… …
640 stall the whole program, and the whole point of using events is to stay 1040 stall the whole program, and the whole point of using events is to stay
641 interactive. 1041 interactive.
642 1042
643 It is fine, however, to call "->recv" when the user of your module 1043 It is fine, however, to call "->recv" when the user of your module
644 requests it (i.e. if you create a http request object ad have a method 1044 requests it (i.e. if you create a http request object ad have a method
645 called "results" that returns the results, it should call "->recv" 1045 called "results" that returns the results, it may call "->recv" freely,
646 freely, as the user of your module knows what she is doing. always). 1046 as the user of your module knows what she is doing. Always).
647 1047
648WHAT TO DO IN THE MAIN PROGRAM 1048WHAT TO DO IN THE MAIN PROGRAM
649 There will always be a single main program - the only place that should 1049 There will always be a single main program - the only place that should
650 dictate which event model to use. 1050 dictate which event model to use.
651 1051
652 If it doesn't care, it can just "use AnyEvent" and use it itself, or not 1052 If the program is not event-based, it need not do anything special, even
653 do anything special (it does not need to be event-based) and let 1053 when it depends on a module that uses an AnyEvent. If the program itself
654 AnyEvent decide which implementation to chose if some module relies on 1054 uses AnyEvent, but does not care which event loop is used, all it needs
655 it. 1055 to do is "use AnyEvent". In either case, AnyEvent will choose the best
1056 available loop implementation.
656 1057
657 If the main program relies on a specific event model - for example, in 1058 If the main program relies on a specific event model - for example, in
658 Gtk2 programs you have to rely on the Glib module - you should load the 1059 Gtk2 programs you have to rely on the Glib module - you should load the
659 event module before loading AnyEvent or any module that uses it: 1060 event module before loading AnyEvent or any module that uses it:
660 generally speaking, you should load it as early as possible. The reason 1061 generally speaking, you should load it as early as possible. The reason
661 is that modules might create watchers when they are loaded, and AnyEvent 1062 is that modules might create watchers when they are loaded, and AnyEvent
662 will decide on the event model to use as soon as it creates watchers, 1063 will decide on the event model to use as soon as it creates watchers,
663 and it might chose the wrong one unless you load the correct one 1064 and it might choose the wrong one unless you load the correct one
664 yourself. 1065 yourself.
665 1066
666 You can chose to use a pure-perl implementation by loading the 1067 You can chose to use a pure-perl implementation by loading the
667 "AnyEvent::Impl::Perl" module, which gives you similar behaviour 1068 "AnyEvent::Loop" module, which gives you similar behaviour everywhere,
668 everywhere, but letting AnyEvent chose the model is generally better. 1069 but letting AnyEvent chose the model is generally better.
669 1070
670 MAINLOOP EMULATION 1071 MAINLOOP EMULATION
671 Sometimes (often for short test scripts, or even standalone programs who 1072 Sometimes (often for short test scripts, or even standalone programs who
672 only want to use AnyEvent), you do not want to run a specific event 1073 only want to use AnyEvent), you do not want to run a specific event
673 loop. 1074 loop.
… …
683 variable somewhere, waiting for it, and sending it when the program 1084 variable somewhere, waiting for it, and sending it when the program
684 should exit cleanly. 1085 should exit cleanly.
685 1086
686OTHER MODULES 1087OTHER MODULES
687 The following is a non-exhaustive list of additional modules that use 1088 The following is a non-exhaustive list of additional modules that use
688 AnyEvent and can therefore be mixed easily with other AnyEvent modules 1089 AnyEvent as a client and can therefore be mixed easily with other
689 in the same program. Some of the modules come with AnyEvent, some are 1090 AnyEvent modules and other event loops in the same program. Some of the
690 available via CPAN. 1091 modules come as part of AnyEvent, the others are available via CPAN (see
1092 <http://search.cpan.org/search?m=module&q=anyevent%3A%3A*> for a longer
1093 non-exhaustive list), and the list is heavily biased towards modules of
1094 the AnyEvent author himself :)
691 1095
692 AnyEvent::Util 1096 AnyEvent::Util (part of the AnyEvent distribution)
693 Contains various utility functions that replace often-used but 1097 Contains various utility functions that replace often-used blocking
694 blocking functions such as "inet_aton" by event-/callback-based 1098 functions such as "inet_aton" with event/callback-based versions.
695 versions.
696 1099
697 AnyEvent::Handle 1100 AnyEvent::Socket (part of the AnyEvent distribution)
698 Provide read and write buffers and manages watchers for reads and
699 writes.
700
701 AnyEvent::Socket
702 Provides various utility functions for (internet protocol) sockets, 1101 Provides various utility functions for (internet protocol) sockets,
703 addresses and name resolution. Also functions to create non-blocking 1102 addresses and name resolution. Also functions to create non-blocking
704 tcp connections or tcp servers, with IPv6 and SRV record support and 1103 tcp connections or tcp servers, with IPv6 and SRV record support and
705 more. 1104 more.
706 1105
707 AnyEvent::DNS 1106 AnyEvent::Handle (part of the AnyEvent distribution)
1107 Provide read and write buffers, manages watchers for reads and
1108 writes, supports raw and formatted I/O, I/O queued and fully
1109 transparent and non-blocking SSL/TLS (via AnyEvent::TLS).
1110
1111 AnyEvent::DNS (part of the AnyEvent distribution)
708 Provides rich asynchronous DNS resolver capabilities. 1112 Provides rich asynchronous DNS resolver capabilities.
709 1113
1114 AnyEvent::HTTP, AnyEvent::IRC, AnyEvent::XMPP, AnyEvent::GPSD,
1115 AnyEvent::IGS, AnyEvent::FCP
1116 Implement event-based interfaces to the protocols of the same name
1117 (for the curious, IGS is the International Go Server and FCP is the
1118 Freenet Client Protocol).
1119
1120 AnyEvent::AIO (part of the AnyEvent distribution)
1121 Truly asynchronous (as opposed to non-blocking) I/O, should be in
1122 the toolbox of every event programmer. AnyEvent::AIO transparently
1123 fuses IO::AIO and AnyEvent together, giving AnyEvent access to
1124 event-based file I/O, and much more.
1125
1126 AnyEvent::Filesys::Notify
1127 AnyEvent is good for non-blocking stuff, but it can't detect file or
1128 path changes (e.g. "watch this directory for new files", "watch this
1129 file for changes"). The AnyEvent::Filesys::Notify module promises to
1130 do just that in a portbale fashion, supporting inotify on GNU/Linux
1131 and some weird, without doubt broken, stuff on OS X to monitor
1132 files. It can fall back to blocking scans at regular intervals
1133 transparently on other platforms, so it's about as portable as it
1134 gets.
1135
1136 (I haven't used it myself, but I haven't heard anybody complaining
1137 about it yet).
1138
1139 AnyEvent::DBI
1140 Executes DBI requests asynchronously in a proxy process for you,
1141 notifying you in an event-based way when the operation is finished.
1142
710 AnyEvent::HTTPD 1143 AnyEvent::HTTPD
711 Provides a simple web application server framework. 1144 A simple embedded webserver.
712 1145
713 AnyEvent::FastPing 1146 AnyEvent::FastPing
714 The fastest ping in the west. 1147 The fastest ping in the west.
715 1148
716 Net::IRC3
717 AnyEvent based IRC client module family.
718
719 Net::XMPP2
720 AnyEvent based XMPP (Jabber protocol) module family.
721
722 Net::FCP
723 AnyEvent-based implementation of the Freenet Client Protocol,
724 birthplace of AnyEvent.
725
726 Event::ExecFlow
727 High level API for event-based execution flow control.
728
729 Coro 1149 Coro
730 Has special support for AnyEvent via Coro::AnyEvent. 1150 Has special support for AnyEvent via Coro::AnyEvent, which allows
1151 you to simply invert the flow control - don't call us, we will call
1152 you:
731 1153
732 AnyEvent::AIO, IO::AIO 1154 async {
733 Truly asynchronous I/O, should be in the toolbox of every event 1155 Coro::AnyEvent::sleep 5; # creates a 5s timer and waits for it
734 programmer. AnyEvent::AIO transparently fuses IO::AIO and AnyEvent 1156 print "5 seconds later!\n";
735 together.
736 1157
737 AnyEvent::BDB, BDB 1158 Coro::AnyEvent::readable *STDIN; # uses an I/O watcher
738 Truly asynchronous Berkeley DB access. AnyEvent::AIO transparently 1159 my $line = <STDIN>; # works for ttys
739 fuses IO::AIO and AnyEvent together.
740 1160
741 IO::Lambda 1161 AnyEvent::HTTP::http_get "url", Coro::rouse_cb;
742 The lambda approach to I/O - don't ask, look there. Can use 1162 my ($body, $hdr) = Coro::rouse_wait;
1163 };
1164
1165SIMPLIFIED AE API
1166 Starting with version 5.0, AnyEvent officially supports a second, much
1167 simpler, API that is designed to reduce the calling, typing and memory
1168 overhead by using function call syntax and a fixed number of parameters.
1169
1170 See the AE manpage for details.
1171
1172ERROR AND EXCEPTION HANDLING
1173 In general, AnyEvent does not do any error handling - it relies on the
1174 caller to do that if required. The AnyEvent::Strict module (see also the
1175 "PERL_ANYEVENT_STRICT" environment variable, below) provides strict
1176 checking of all AnyEvent methods, however, which is highly useful during
1177 development.
1178
1179 As for exception handling (i.e. runtime errors and exceptions thrown
1180 while executing a callback), this is not only highly event-loop
1181 specific, but also not in any way wrapped by this module, as this is the
1182 job of the main program.
1183
1184 The pure perl event loop simply re-throws the exception (usually within
1185 "condvar->recv"), the Event and EV modules call "$Event/EV::DIED->()",
1186 Glib uses "install_exception_handler" and so on.
1187
1188ENVIRONMENT VARIABLES
1189 AnyEvent supports a number of environment variables that tune the
1190 runtime behaviour. They are usually evaluated when AnyEvent is loaded,
1191 initialised, or a submodule that uses them is loaded. Many of them also
1192 cause AnyEvent to load additional modules - for example,
1193 "PERL_ANYEVENT_DEBUG_WRAP" causes the AnyEvent::Debug module to be
1194 loaded.
1195
1196 All the environment variables documented here start with
1197 "PERL_ANYEVENT_", which is what AnyEvent considers its own namespace.
1198 Other modules are encouraged (but by no means required) to use
1199 "PERL_ANYEVENT_SUBMODULE" if they have registered the
1200 AnyEvent::Submodule namespace on CPAN, for any submodule. For example,
1201 AnyEvent::HTTP could be expected to use "PERL_ANYEVENT_HTTP_PROXY" (it
1202 should not access env variables starting with "AE_", see below).
1203
1204 All variables can also be set via the "AE_" prefix, that is, instead of
1205 setting "PERL_ANYEVENT_VERBOSE" you can also set "AE_VERBOSE". In case
1206 there is a clash btween anyevent and another program that uses
1207 "AE_something" you can set the corresponding "PERL_ANYEVENT_something"
1208 variable to the empty string, as those variables take precedence.
1209
1210 When AnyEvent is first loaded, it copies all "AE_xxx" env variables to
1211 their "PERL_ANYEVENT_xxx" counterpart unless that variable already
1212 exists. If taint mode is on, then AnyEvent will remove *all* environment
1213 variables starting with "PERL_ANYEVENT_" from %ENV (or replace them with
1214 "undef" or the empty string, if the corresaponding "AE_" variable is
1215 set).
1216
1217 The exact algorithm is currently:
1218
1219 1. if taint mode enabled, delete all PERL_ANYEVENT_xyz variables from %ENV
1220 2. copy over AE_xyz to PERL_ANYEVENT_xyz unless the latter alraedy exists
1221 3. if taint mode enabled, set all PERL_ANYEVENT_xyz variables to undef.
1222
1223 This ensures that child processes will not see the "AE_" variables.
1224
1225 The following environment variables are currently known to AnyEvent:
1226
1227 "PERL_ANYEVENT_VERBOSE"
1228 By default, AnyEvent will log messages with loglevel 4 ("error") or
1229 higher (see AnyEvent::Log). You can set this environment variable to
1230 a numerical loglevel to make AnyEvent more (or less) talkative.
1231
1232 If you want to do more than just set the global logging level you
1233 should have a look at "PERL_ANYEVENT_LOG", which allows much more
1234 complex specifications.
1235
1236 When set to 0 ("off"), then no messages whatsoever will be logged
1237 with everything else at defaults.
1238
1239 When set to 5 or higher ("warn"), AnyEvent warns about unexpected
1240 conditions, such as not being able to load the event model specified
1241 by "PERL_ANYEVENT_MODEL", or a guard callback throwing an exception
1242 - this is the minimum recommended level for use during development.
1243
1244 When set to 7 or higher (info), AnyEvent reports which event model
1245 it chooses.
1246
1247 When set to 8 or higher (debug), then AnyEvent will report extra
1248 information on which optional modules it loads and how it implements
1249 certain features.
1250
1251 "PERL_ANYEVENT_LOG"
1252 Accepts rather complex logging specifications. For example, you
1253 could log all "debug" messages of some module to stderr, warnings
1254 and above to stderr, and errors and above to syslog, with:
1255
1256 PERL_ANYEVENT_LOG=Some::Module=debug,+log:filter=warn,+%syslog:%syslog=error,syslog
1257
1258 For the rather extensive details, see AnyEvent::Log.
1259
1260 This variable is evaluated when AnyEvent (or AnyEvent::Log) is
1261 loaded, so will take effect even before AnyEvent has initialised
1262 itself.
1263
1264 Note that specifying this environment variable causes the
1265 AnyEvent::Log module to be loaded, while "PERL_ANYEVENT_VERBOSE"
1266 does not, so only using the latter saves a few hundred kB of memory
1267 unless a module explicitly needs the extra features of
743 AnyEvent. 1268 AnyEvent::Log.
1269
1270 "PERL_ANYEVENT_STRICT"
1271 AnyEvent does not do much argument checking by default, as thorough
1272 argument checking is very costly. Setting this variable to a true
1273 value will cause AnyEvent to load "AnyEvent::Strict" and then to
1274 thoroughly check the arguments passed to most method calls. If it
1275 finds any problems, it will croak.
1276
1277 In other words, enables "strict" mode.
1278
1279 Unlike "use strict" (or its modern cousin, "use common::sense", it
1280 is definitely recommended to keep it off in production. Keeping
1281 "PERL_ANYEVENT_STRICT=1" in your environment while developing
1282 programs can be very useful, however.
1283
1284 "PERL_ANYEVENT_DEBUG_SHELL"
1285 If this env variable is nonempty, then its contents will be
1286 interpreted by "AnyEvent::Socket::parse_hostport" and
1287 "AnyEvent::Debug::shell" (after replacing every occurance of $$ by
1288 the process pid). The shell object is saved in
1289 $AnyEvent::Debug::SHELL.
1290
1291 This happens when the first watcher is created.
1292
1293 For example, to bind a debug shell on a unix domain socket in
1294 /tmp/debug<pid>.sock, you could use this:
1295
1296 PERL_ANYEVENT_DEBUG_SHELL=/tmp/debug\$\$.sock perlprog
1297 # connect with e.g.: socat readline /tmp/debug123.sock
1298
1299 Or to bind to tcp port 4545 on localhost:
1300
1301 PERL_ANYEVENT_DEBUG_SHELL=127.0.0.1:4545 perlprog
1302 # connect with e.g.: telnet localhost 4545
1303
1304 Note that creating sockets in /tmp or on localhost is very unsafe on
1305 multiuser systems.
1306
1307 "PERL_ANYEVENT_DEBUG_WRAP"
1308 Can be set to 0, 1 or 2 and enables wrapping of all watchers for
1309 debugging purposes. See "AnyEvent::Debug::wrap" for details.
1310
1311 "PERL_ANYEVENT_MODEL"
1312 This can be used to specify the event model to be used by AnyEvent,
1313 before auto detection and -probing kicks in.
1314
1315 It normally is a string consisting entirely of ASCII letters (e.g.
1316 "EV" or "IOAsync"). The string "AnyEvent::Impl::" gets prepended and
1317 the resulting module name is loaded and - if the load was successful
1318 - used as event model backend. If it fails to load then AnyEvent
1319 will proceed with auto detection and -probing.
1320
1321 If the string ends with "::" instead (e.g. "AnyEvent::Impl::EV::")
1322 then nothing gets prepended and the module name is used as-is (hint:
1323 "::" at the end of a string designates a module name and quotes it
1324 appropriately).
1325
1326 For example, to force the pure perl model (AnyEvent::Loop::Perl) you
1327 could start your program like this:
1328
1329 PERL_ANYEVENT_MODEL=Perl perl ...
1330
1331 "PERL_ANYEVENT_IO_MODEL"
1332 The current file I/O model - see AnyEvent::IO for more info.
1333
1334 At the moment, only "Perl" (small, pure-perl, synchronous) and
1335 "IOAIO" (truly asynchronous) are supported. The default is "IOAIO"
1336 if AnyEvent::AIO can be loaded, otherwise it is "Perl".
1337
1338 "PERL_ANYEVENT_PROTOCOLS"
1339 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
1340 preferences for IPv4 or IPv6. The default is unspecified (and might
1341 change, or be the result of auto probing).
1342
1343 Must be set to a comma-separated list of protocols or address
1344 families, current supported: "ipv4" and "ipv6". Only protocols
1345 mentioned will be used, and preference will be given to protocols
1346 mentioned earlier in the list.
1347
1348 This variable can effectively be used for denial-of-service attacks
1349 against local programs (e.g. when setuid), although the impact is
1350 likely small, as the program has to handle conenction and other
1351 failures anyways.
1352
1353 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
1354 IPv6, but support both and try to use both.
1355 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
1356 resolve or contact IPv6 addresses.
1357 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
1358 prefer IPv6 over IPv4.
1359
1360 "PERL_ANYEVENT_HOSTS"
1361 This variable, if specified, overrides the /etc/hosts file used by
1362 AnyEvent::Socket"::resolve_sockaddr", i.e. hosts aliases will be
1363 read from that file instead.
1364
1365 "PERL_ANYEVENT_EDNS0"
1366 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
1367 for DNS. This extension is generally useful to reduce DNS traffic,
1368 especially when DNSSEC is involved, but some (broken) firewalls drop
1369 such DNS packets, which is why it is off by default.
1370
1371 Setting this variable to 1 will cause AnyEvent::DNS to announce
1372 EDNS0 in its DNS requests.
1373
1374 "PERL_ANYEVENT_MAX_FORKS"
1375 The maximum number of child processes that
1376 "AnyEvent::Util::fork_call" will create in parallel.
1377
1378 "PERL_ANYEVENT_MAX_OUTSTANDING_DNS"
1379 The default value for the "max_outstanding" parameter for the
1380 default DNS resolver - this is the maximum number of parallel DNS
1381 requests that are sent to the DNS server.
1382
1383 "PERL_ANYEVENT_MAX_SIGNAL_LATENCY"
1384 Perl has inherently racy signal handling (you can basically choose
1385 between losing signals and memory corruption) - pure perl event
1386 loops (including "AnyEvent::Loop", when "Async::Interrupt" isn't
1387 available) therefore have to poll regularly to avoid losing signals.
1388
1389 Some event loops are racy, but don't poll regularly, and some event
1390 loops are written in C but are still racy. For those event loops,
1391 AnyEvent installs a timer that regularly wakes up the event loop.
1392
1393 By default, the interval for this timer is 10 seconds, but you can
1394 override this delay with this environment variable (or by setting
1395 the $AnyEvent::MAX_SIGNAL_LATENCY variable before creating signal
1396 watchers).
1397
1398 Lower values increase CPU (and energy) usage, higher values can
1399 introduce long delays when reaping children or waiting for signals.
1400
1401 The AnyEvent::Async module, if available, will be used to avoid this
1402 polling (with most event loops).
1403
1404 "PERL_ANYEVENT_RESOLV_CONF"
1405 The absolute path to a resolv.conf-style file to use instead of
1406 /etc/resolv.conf (or the OS-specific configuration) in the default
1407 resolver, or the empty string to select the default configuration.
1408
1409 "PERL_ANYEVENT_CA_FILE", "PERL_ANYEVENT_CA_PATH".
1410 When neither "ca_file" nor "ca_path" was specified during
1411 AnyEvent::TLS context creation, and either of these environment
1412 variables are nonempty, they will be used to specify CA certificate
1413 locations instead of a system-dependent default.
1414
1415 "PERL_ANYEVENT_AVOID_GUARD" and "PERL_ANYEVENT_AVOID_ASYNC_INTERRUPT"
1416 When these are set to 1, then the respective modules are not loaded.
1417 Mostly good for testing AnyEvent itself.
744 1418
745SUPPLYING YOUR OWN EVENT MODEL INTERFACE 1419SUPPLYING YOUR OWN EVENT MODEL INTERFACE
746 This is an advanced topic that you do not normally need to use AnyEvent 1420 This is an advanced topic that you do not normally need to use AnyEvent
747 in a module. This section is only of use to event loop authors who want 1421 in a module. This section is only of use to event loop authors who want
748 to provide AnyEvent compatibility. 1422 to provide AnyEvent compatibility.
… …
782 1456
783 *rxvt-unicode* also cheats a bit by not providing blocking access to 1457 *rxvt-unicode* also cheats a bit by not providing blocking access to
784 condition variables: code blocking while waiting for a condition will 1458 condition variables: code blocking while waiting for a condition will
785 "die". This still works with most modules/usages, and blocking calls 1459 "die". This still works with most modules/usages, and blocking calls
786 must not be done in an interactive application, so it makes sense. 1460 must not be done in an interactive application, so it makes sense.
787
788ENVIRONMENT VARIABLES
789 The following environment variables are used by this module:
790
791 "PERL_ANYEVENT_VERBOSE"
792 By default, AnyEvent will be completely silent except in fatal
793 conditions. You can set this environment variable to make AnyEvent
794 more talkative.
795
796 When set to 1 or higher, causes AnyEvent to warn about unexpected
797 conditions, such as not being able to load the event model specified
798 by "PERL_ANYEVENT_MODEL".
799
800 When set to 2 or higher, cause AnyEvent to report to STDERR which
801 event model it chooses.
802
803 "PERL_ANYEVENT_MODEL"
804 This can be used to specify the event model to be used by AnyEvent,
805 before auto detection and -probing kicks in. It must be a string
806 consisting entirely of ASCII letters. The string "AnyEvent::Impl::"
807 gets prepended and the resulting module name is loaded and if the
808 load was successful, used as event model. If it fails to load
809 AnyEvent will proceed with auto detection and -probing.
810
811 This functionality might change in future versions.
812
813 For example, to force the pure perl model (AnyEvent::Impl::Perl) you
814 could start your program like this:
815
816 PERL_ANYEVENT_MODEL=Perl perl ...
817
818 "PERL_ANYEVENT_PROTOCOLS"
819 Used by both AnyEvent::DNS and AnyEvent::Socket to determine
820 preferences for IPv4 or IPv6. The default is unspecified (and might
821 change, or be the result of auto probing).
822
823 Must be set to a comma-separated list of protocols or address
824 families, current supported: "ipv4" and "ipv6". Only protocols
825 mentioned will be used, and preference will be given to protocols
826 mentioned earlier in the list.
827
828 This variable can effectively be used for denial-of-service attacks
829 against local programs (e.g. when setuid), although the impact is
830 likely small, as the program has to handle connection errors
831 already-
832
833 Examples: "PERL_ANYEVENT_PROTOCOLS=ipv4,ipv6" - prefer IPv4 over
834 IPv6, but support both and try to use both.
835 "PERL_ANYEVENT_PROTOCOLS=ipv4" - only support IPv4, never try to
836 resolve or contact IPv6 addresses.
837 "PERL_ANYEVENT_PROTOCOLS=ipv6,ipv4" support either IPv4 or IPv6, but
838 prefer IPv6 over IPv4.
839
840 "PERL_ANYEVENT_EDNS0"
841 Used by AnyEvent::DNS to decide whether to use the EDNS0 extension
842 for DNS. This extension is generally useful to reduce DNS traffic,
843 but some (broken) firewalls drop such DNS packets, which is why it
844 is off by default.
845
846 Setting this variable to 1 will cause AnyEvent::DNS to announce
847 EDNS0 in its DNS requests.
848
849 "PERL_ANYEVENT_MAX_FORKS"
850 The maximum number of child processes that
851 "AnyEvent::Util::fork_call" will create in parallel.
852 1461
853EXAMPLE PROGRAM 1462EXAMPLE PROGRAM
854 The following program uses an I/O watcher to read data from STDIN, a 1463 The following program uses an I/O watcher to read data from STDIN, a
855 timer to display a message once per second, and a condition variable to 1464 timer to display a message once per second, and a condition variable to
856 quit the program when the user enters quit: 1465 quit the program when the user enters quit:
… …
868 warn "read: $input\n"; # output what has been read 1477 warn "read: $input\n"; # output what has been read
869 $cv->send if $input =~ /^q/i; # quit program if /^q/i 1478 $cv->send if $input =~ /^q/i; # quit program if /^q/i
870 }, 1479 },
871 ); 1480 );
872 1481
873 my $time_watcher; # can only be used once
874
875 sub new_timer {
876 $timer = AnyEvent->timer (after => 1, cb => sub { 1482 my $time_watcher = AnyEvent->timer (after => 1, interval => 1, cb => sub {
877 warn "timeout\n"; # print 'timeout' about every second 1483 warn "timeout\n"; # print 'timeout' at most every second
878 &new_timer; # and restart the time
879 });
880 } 1484 });
881
882 new_timer; # create first timer
883 1485
884 $cv->recv; # wait until user enters /^q/i 1486 $cv->recv; # wait until user enters /^q/i
885 1487
886REAL-WORLD EXAMPLE 1488REAL-WORLD EXAMPLE
887 Consider the Net::FCP module. It features (among others) the following 1489 Consider the Net::FCP module. It features (among others) the following
… …
959 1561
960 The actual code goes further and collects all errors ("die"s, 1562 The actual code goes further and collects all errors ("die"s,
961 exceptions) that occurred during request processing. The "result" method 1563 exceptions) that occurred during request processing. The "result" method
962 detects whether an exception as thrown (it is stored inside the $txn 1564 detects whether an exception as thrown (it is stored inside the $txn
963 object) and just throws the exception, which means connection errors and 1565 object) and just throws the exception, which means connection errors and
964 other problems get reported tot he code that tries to use the result, 1566 other problems get reported to the code that tries to use the result,
965 not in a random callback. 1567 not in a random callback.
966 1568
967 All of this enables the following usage styles: 1569 All of this enables the following usage styles:
968 1570
969 1. Blocking: 1571 1. Blocking:
… …
1014 through AnyEvent. The benchmark creates a lot of timers (with a zero 1616 through AnyEvent. The benchmark creates a lot of timers (with a zero
1015 timeout) and I/O watchers (watching STDOUT, a pty, to become writable, 1617 timeout) and I/O watchers (watching STDOUT, a pty, to become writable,
1016 which it is), lets them fire exactly once and destroys them again. 1618 which it is), lets them fire exactly once and destroys them again.
1017 1619
1018 Source code for this benchmark is found as eg/bench in the AnyEvent 1620 Source code for this benchmark is found as eg/bench in the AnyEvent
1019 distribution. 1621 distribution. It uses the AE interface, which makes a real difference
1622 for the EV and Perl backends only.
1020 1623
1021 Explanation of the columns 1624 Explanation of the columns
1022 *watcher* is the number of event watchers created/destroyed. Since 1625 *watcher* is the number of event watchers created/destroyed. Since
1023 different event models feature vastly different performances, each event 1626 different event models feature vastly different performances, each event
1024 loop was given a number of watchers so that overall runtime is 1627 loop was given a number of watchers so that overall runtime is
… …
1043 *destroy* is the time, in microseconds, that it takes to destroy a 1646 *destroy* is the time, in microseconds, that it takes to destroy a
1044 single watcher. 1647 single watcher.
1045 1648
1046 Results 1649 Results
1047 name watchers bytes create invoke destroy comment 1650 name watchers bytes create invoke destroy comment
1048 EV/EV 400000 244 0.56 0.46 0.31 EV native interface 1651 EV/EV 100000 223 0.47 0.43 0.27 EV native interface
1049 EV/Any 100000 244 2.50 0.46 0.29 EV + AnyEvent watchers 1652 EV/Any 100000 223 0.48 0.42 0.26 EV + AnyEvent watchers
1050 CoroEV/Any 100000 244 2.49 0.44 0.29 coroutines + Coro::Signal 1653 Coro::EV/Any 100000 223 0.47 0.42 0.26 coroutines + Coro::Signal
1051 Perl/Any 100000 513 4.92 0.87 1.12 pure perl implementation 1654 Perl/Any 100000 431 2.70 0.74 0.92 pure perl implementation
1052 Event/Event 16000 516 31.88 31.30 0.85 Event native interface 1655 Event/Event 16000 516 31.16 31.84 0.82 Event native interface
1053 Event/Any 16000 590 35.75 31.42 1.08 Event + AnyEvent watchers 1656 Event/Any 16000 1203 42.61 34.79 1.80 Event + AnyEvent watchers
1657 IOAsync/Any 16000 1911 41.92 27.45 16.81 via IO::Async::Loop::IO_Poll
1658 IOAsync/Any 16000 1726 40.69 26.37 15.25 via IO::Async::Loop::Epoll
1054 Glib/Any 16000 1357 98.22 12.41 54.00 quadratic behaviour 1659 Glib/Any 16000 1118 89.00 12.57 51.17 quadratic behaviour
1055 Tk/Any 2000 1860 26.97 67.98 14.00 SEGV with >> 2000 watchers 1660 Tk/Any 2000 1346 20.96 10.75 8.00 SEGV with >> 2000 watchers
1056 POE/Event 2000 6644 108.64 736.02 14.73 via POE::Loop::Event 1661 POE/Any 2000 6951 108.97 795.32 14.24 via POE::Loop::Event
1057 POE/Select 2000 6343 94.13 809.12 565.96 via POE::Loop::Select 1662 POE/Any 2000 6648 94.79 774.40 575.51 via POE::Loop::Select
1058 1663
1059 Discussion 1664 Discussion
1060 The benchmark does *not* measure scalability of the event loop very 1665 The benchmark does *not* measure scalability of the event loop very
1061 well. For example, a select-based event loop (such as the pure perl one) 1666 well. For example, a select-based event loop (such as the pure perl one)
1062 can never compete with an event loop that uses epoll when the number of 1667 can never compete with an event loop that uses epoll when the number of
… …
1073 benchmark machine, handling an event takes roughly 1600 CPU cycles with 1678 benchmark machine, handling an event takes roughly 1600 CPU cycles with
1074 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000 1679 EV, 3100 CPU cycles with AnyEvent's pure perl loop and almost 3000000
1075 CPU cycles with POE. 1680 CPU cycles with POE.
1076 1681
1077 "EV" is the sole leader regarding speed and memory use, which are both 1682 "EV" is the sole leader regarding speed and memory use, which are both
1078 maximal/minimal, respectively. Even when going through AnyEvent, it uses 1683 maximal/minimal, respectively. When using the AE API there is zero
1684 overhead (when going through the AnyEvent API create is about 5-6 times
1685 slower, with other times being equal, so still uses far less memory than
1079 far less memory than any other event loop and is still faster than Event 1686 any other event loop and is still faster than Event natively).
1080 natively.
1081 1687
1082 The pure perl implementation is hit in a few sweet spots (both the 1688 The pure perl implementation is hit in a few sweet spots (both the
1083 constant timeout and the use of a single fd hit optimisations in the 1689 constant timeout and the use of a single fd hit optimisations in the
1084 perl interpreter and the backend itself). Nevertheless this shows that 1690 perl interpreter and the backend itself). Nevertheless this shows that
1085 it adds very little overhead in itself. Like any select-based backend 1691 it adds very little overhead in itself. Like any select-based backend
… …
1087 few of them active), of course, but this was not subject of this 1693 few of them active), of course, but this was not subject of this
1088 benchmark. 1694 benchmark.
1089 1695
1090 The "Event" module has a relatively high setup and callback invocation 1696 The "Event" module has a relatively high setup and callback invocation
1091 cost, but overall scores in on the third place. 1697 cost, but overall scores in on the third place.
1698
1699 "IO::Async" performs admirably well, about on par with "Event", even
1700 when using its pure perl backend.
1092 1701
1093 "Glib"'s memory usage is quite a bit higher, but it features a faster 1702 "Glib"'s memory usage is quite a bit higher, but it features a faster
1094 callback invocation and overall ends up in the same class as "Event". 1703 callback invocation and overall ends up in the same class as "Event".
1095 However, Glib scales extremely badly, doubling the number of watchers 1704 However, Glib scales extremely badly, doubling the number of watchers
1096 increases the processing time by more than a factor of four, making it 1705 increases the processing time by more than a factor of four, making it
… …
1128 when used without AnyEvent), but most event loops have acceptable 1737 when used without AnyEvent), but most event loops have acceptable
1129 performance with or without AnyEvent. 1738 performance with or without AnyEvent.
1130 1739
1131 * The overhead AnyEvent adds is usually much smaller than the overhead 1740 * The overhead AnyEvent adds is usually much smaller than the overhead
1132 of the actual event loop, only with extremely fast event loops such 1741 of the actual event loop, only with extremely fast event loops such
1133 as EV adds AnyEvent significant overhead. 1742 as EV does AnyEvent add significant overhead.
1134 1743
1135 * You should avoid POE like the plague if you want performance or 1744 * You should avoid POE like the plague if you want performance or
1136 reasonable memory usage. 1745 reasonable memory usage.
1137 1746
1138 BENCHMARKING THE LARGE SERVER CASE 1747 BENCHMARKING THE LARGE SERVER CASE
… …
1152 In this benchmark, we use 10000 socket pairs (20000 sockets), of which 1761 In this benchmark, we use 10000 socket pairs (20000 sockets), of which
1153 100 (1%) are active. This mirrors the activity of large servers with 1762 100 (1%) are active. This mirrors the activity of large servers with
1154 many connections, most of which are idle at any one point in time. 1763 many connections, most of which are idle at any one point in time.
1155 1764
1156 Source code for this benchmark is found as eg/bench2 in the AnyEvent 1765 Source code for this benchmark is found as eg/bench2 in the AnyEvent
1157 distribution. 1766 distribution. It uses the AE interface, which makes a real difference
1767 for the EV and Perl backends only.
1158 1768
1159 Explanation of the columns 1769 Explanation of the columns
1160 *sockets* is the number of sockets, and twice the number of "servers" 1770 *sockets* is the number of sockets, and twice the number of "servers"
1161 (as each server has a read and write socket end). 1771 (as each server has a read and write socket end).
1162 1772
… …
1167 single "request", that is, reading the token from the pipe and 1777 single "request", that is, reading the token from the pipe and
1168 forwarding it to another server. This includes deleting the old timeout 1778 forwarding it to another server. This includes deleting the old timeout
1169 and creating a new one that moves the timeout into the future. 1779 and creating a new one that moves the timeout into the future.
1170 1780
1171 Results 1781 Results
1172 name sockets create request 1782 name sockets create request
1173 EV 20000 69.01 11.16 1783 EV 20000 62.66 7.99
1174 Perl 20000 73.32 35.87 1784 Perl 20000 68.32 32.64
1175 Event 20000 212.62 257.32 1785 IOAsync 20000 174.06 101.15 epoll
1176 Glib 20000 651.16 1896.30 1786 IOAsync 20000 174.67 610.84 poll
1787 Event 20000 202.69 242.91
1788 Glib 20000 557.01 1689.52
1177 POE 20000 349.67 12317.24 uses POE::Loop::Event 1789 POE 20000 341.54 12086.32 uses POE::Loop::Event
1178 1790
1179 Discussion 1791 Discussion
1180 This benchmark *does* measure scalability and overall performance of the 1792 This benchmark *does* measure scalability and overall performance of the
1181 particular event loop. 1793 particular event loop.
1182 1794
1183 EV is again fastest. Since it is using epoll on my system, the setup 1795 EV is again fastest. Since it is using epoll on my system, the setup
1184 time is relatively high, though. 1796 time is relatively high, though.
1185 1797
1186 Perl surprisingly comes second. It is much faster than the C-based event 1798 Perl surprisingly comes second. It is much faster than the C-based event
1187 loops Event and Glib. 1799 loops Event and Glib.
1800
1801 IO::Async performs very well when using its epoll backend, and still
1802 quite good compared to Glib when using its pure perl backend.
1188 1803
1189 Event suffers from high setup time as well (look at its code and you 1804 Event suffers from high setup time as well (look at its code and you
1190 will understand why). Callback invocation also has a high overhead 1805 will understand why). Callback invocation also has a high overhead
1191 compared to the "$_->() for .."-style loop that the Perl event loop 1806 compared to the "$_->() for .."-style loop that the Perl event loop
1192 uses. Event uses select or poll in basically all documented 1807 uses. Event uses select or poll in basically all documented
… …
1243 1858
1244 Summary 1859 Summary
1245 * C-based event loops perform very well with small number of watchers, 1860 * C-based event loops perform very well with small number of watchers,
1246 as the management overhead dominates. 1861 as the management overhead dominates.
1247 1862
1863 THE IO::Lambda BENCHMARK
1864 Recently I was told about the benchmark in the IO::Lambda manpage, which
1865 could be misinterpreted to make AnyEvent look bad. In fact, the
1866 benchmark simply compares IO::Lambda with POE, and IO::Lambda looks
1867 better (which shouldn't come as a surprise to anybody). As such, the
1868 benchmark is fine, and mostly shows that the AnyEvent backend from
1869 IO::Lambda isn't very optimal. But how would AnyEvent compare when used
1870 without the extra baggage? To explore this, I wrote the equivalent
1871 benchmark for AnyEvent.
1872
1873 The benchmark itself creates an echo-server, and then, for 500 times,
1874 connects to the echo server, sends a line, waits for the reply, and then
1875 creates the next connection. This is a rather bad benchmark, as it
1876 doesn't test the efficiency of the framework or much non-blocking I/O,
1877 but it is a benchmark nevertheless.
1878
1879 name runtime
1880 Lambda/select 0.330 sec
1881 + optimized 0.122 sec
1882 Lambda/AnyEvent 0.327 sec
1883 + optimized 0.138 sec
1884 Raw sockets/select 0.077 sec
1885 POE/select, components 0.662 sec
1886 POE/select, raw sockets 0.226 sec
1887 POE/select, optimized 0.404 sec
1888
1889 AnyEvent/select/nb 0.085 sec
1890 AnyEvent/EV/nb 0.068 sec
1891 +state machine 0.134 sec
1892
1893 The benchmark is also a bit unfair (my fault): the IO::Lambda/POE
1894 benchmarks actually make blocking connects and use 100% blocking I/O,
1895 defeating the purpose of an event-based solution. All of the newly
1896 written AnyEvent benchmarks use 100% non-blocking connects (using
1897 AnyEvent::Socket::tcp_connect and the asynchronous pure perl DNS
1898 resolver), so AnyEvent is at a disadvantage here, as non-blocking
1899 connects generally require a lot more bookkeeping and event handling
1900 than blocking connects (which involve a single syscall only).
1901
1902 The last AnyEvent benchmark additionally uses AnyEvent::Handle, which
1903 offers similar expressive power as POE and IO::Lambda, using
1904 conventional Perl syntax. This means that both the echo server and the
1905 client are 100% non-blocking, further placing it at a disadvantage.
1906
1907 As you can see, the AnyEvent + EV combination even beats the
1908 hand-optimised "raw sockets benchmark", while AnyEvent + its pure perl
1909 backend easily beats IO::Lambda and POE.
1910
1911 And even the 100% non-blocking version written using the high-level (and
1912 slow :) AnyEvent::Handle abstraction beats both POE and IO::Lambda
1913 higher level ("unoptimised") abstractions by a large margin, even though
1914 it does all of DNS, tcp-connect and socket I/O in a non-blocking way.
1915
1916 The two AnyEvent benchmarks programs can be found as eg/ae0.pl and
1917 eg/ae2.pl in the AnyEvent distribution, the remaining benchmarks are
1918 part of the IO::Lambda distribution and were used without any changes.
1919
1920SIGNALS
1921 AnyEvent currently installs handlers for these signals:
1922
1923 SIGCHLD
1924 A handler for "SIGCHLD" is installed by AnyEvent's child watcher
1925 emulation for event loops that do not support them natively. Also,
1926 some event loops install a similar handler.
1927
1928 Additionally, when AnyEvent is loaded and SIGCHLD is set to IGNORE,
1929 then AnyEvent will reset it to default, to avoid losing child exit
1930 statuses.
1931
1932 SIGPIPE
1933 A no-op handler is installed for "SIGPIPE" when $SIG{PIPE} is
1934 "undef" when AnyEvent gets loaded.
1935
1936 The rationale for this is that AnyEvent users usually do not really
1937 depend on SIGPIPE delivery (which is purely an optimisation for
1938 shell use, or badly-written programs), but "SIGPIPE" can cause
1939 spurious and rare program exits as a lot of people do not expect
1940 "SIGPIPE" when writing to some random socket.
1941
1942 The rationale for installing a no-op handler as opposed to ignoring
1943 it is that this way, the handler will be restored to defaults on
1944 exec.
1945
1946 Feel free to install your own handler, or reset it to defaults.
1947
1948RECOMMENDED/OPTIONAL MODULES
1949 One of AnyEvent's main goals is to be 100% Pure-Perl(tm): only perl (and
1950 its built-in modules) are required to use it.
1951
1952 That does not mean that AnyEvent won't take advantage of some additional
1953 modules if they are installed.
1954
1955 This section explains which additional modules will be used, and how
1956 they affect AnyEvent's operation.
1957
1958 Async::Interrupt
1959 This slightly arcane module is used to implement fast signal
1960 handling: To my knowledge, there is no way to do completely
1961 race-free and quick signal handling in pure perl. To ensure that
1962 signals still get delivered, AnyEvent will start an interval timer
1963 to wake up perl (and catch the signals) with some delay (default is
1964 10 seconds, look for $AnyEvent::MAX_SIGNAL_LATENCY).
1965
1966 If this module is available, then it will be used to implement
1967 signal catching, which means that signals will not be delayed, and
1968 the event loop will not be interrupted regularly, which is more
1969 efficient (and good for battery life on laptops).
1970
1971 This affects not just the pure-perl event loop, but also other event
1972 loops that have no signal handling on their own (e.g. Glib, Tk, Qt).
1973
1974 Some event loops (POE, Event, Event::Lib) offer signal watchers
1975 natively, and either employ their own workarounds (POE) or use
1976 AnyEvent's workaround (using $AnyEvent::MAX_SIGNAL_LATENCY).
1977 Installing Async::Interrupt does nothing for those backends.
1978
1979 EV This module isn't really "optional", as it is simply one of the
1980 backend event loops that AnyEvent can use. However, it is simply the
1981 best event loop available in terms of features, speed and stability:
1982 It supports the AnyEvent API optimally, implements all the watcher
1983 types in XS, does automatic timer adjustments even when no monotonic
1984 clock is available, can take avdantage of advanced kernel interfaces
1985 such as "epoll" and "kqueue", and is the fastest backend *by far*.
1986 You can even embed Glib/Gtk2 in it (or vice versa, see EV::Glib and
1987 Glib::EV).
1988
1989 If you only use backends that rely on another event loop (e.g.
1990 "Tk"), then this module will do nothing for you.
1991
1992 Guard
1993 The guard module, when used, will be used to implement
1994 "AnyEvent::Util::guard". This speeds up guards considerably (and
1995 uses a lot less memory), but otherwise doesn't affect guard
1996 operation much. It is purely used for performance.
1997
1998 JSON and JSON::XS
1999 One of these modules is required when you want to read or write JSON
2000 data via AnyEvent::Handle. JSON is also written in pure-perl, but
2001 can take advantage of the ultra-high-speed JSON::XS module when it
2002 is installed.
2003
2004 Net::SSLeay
2005 Implementing TLS/SSL in Perl is certainly interesting, but not very
2006 worthwhile: If this module is installed, then AnyEvent::Handle (with
2007 the help of AnyEvent::TLS), gains the ability to do TLS/SSL.
2008
2009 Time::HiRes
2010 This module is part of perl since release 5.008. It will be used
2011 when the chosen event library does not come with a timing source of
2012 its own. The pure-perl event loop (AnyEvent::Loop) will additionally
2013 load it to try to use a monotonic clock for timing stability.
2014
2015 AnyEvent::AIO (and IO::AIO)
2016 The default implementation of AnyEvent::IO is to do I/O
2017 synchronously, stopping programs while they access the disk, which
2018 is fine for a lot of programs.
2019
2020 Installing AnyEvent::AIO (and its IO::AIO dependency) makes it
2021 switch to a true asynchronous implementation, so event processing
2022 can continue even while waiting for disk I/O.
2023
1248FORK 2024FORK
1249 Most event libraries are not fork-safe. The ones who are usually are 2025 Most event libraries are not fork-safe. The ones who are usually are
1250 because they rely on inefficient but fork-safe "select" or "poll" calls. 2026 because they rely on inefficient but fork-safe "select" or "poll" calls
1251 Only EV is fully fork-aware. 2027 - higher performance APIs such as BSD's kqueue or the dreaded Linux
2028 epoll are usually badly thought-out hacks that are incompatible with
2029 fork in one way or another. Only EV is fully fork-aware and ensures that
2030 you continue event-processing in both parent and child (or both, if you
2031 know what you are doing).
2032
2033 This means that, in general, you cannot fork and do event processing in
2034 the child if the event library was initialised before the fork (which
2035 usually happens when the first AnyEvent watcher is created, or the
2036 library is loaded).
1252 2037
1253 If you have to fork, you must either do so *before* creating your first 2038 If you have to fork, you must either do so *before* creating your first
1254 watcher OR you must not use AnyEvent at all in the child. 2039 watcher OR you must not use AnyEvent at all in the child OR you must do
2040 something completely out of the scope of AnyEvent.
2041
2042 The problem of doing event processing in the parent *and* the child is
2043 much more complicated: even for backends that *are* fork-aware or
2044 fork-safe, their behaviour is not usually what you want: fork clones all
2045 watchers, that means all timers, I/O watchers etc. are active in both
2046 parent and child, which is almost never what you want. USing "exec" to
2047 start worker children from some kind of manage rprocess is usually
2048 preferred, because it is much easier and cleaner, at the expense of
2049 having to have another binary.
1255 2050
1256SECURITY CONSIDERATIONS 2051SECURITY CONSIDERATIONS
1257 AnyEvent can be forced to load any event model via 2052 AnyEvent can be forced to load any event model via
1258 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used 2053 $ENV{PERL_ANYEVENT_MODEL}. While this cannot (to my knowledge) be used
1259 to execute arbitrary code or directly gain access, it can easily be used 2054 to execute arbitrary code or directly gain access, it can easily be used
… …
1262 model than specified in the variable. 2057 model than specified in the variable.
1263 2058
1264 You can make AnyEvent completely ignore this variable by deleting it 2059 You can make AnyEvent completely ignore this variable by deleting it
1265 before the first watcher gets created, e.g. with a "BEGIN" block: 2060 before the first watcher gets created, e.g. with a "BEGIN" block:
1266 2061
1267 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} } 2062 BEGIN { delete $ENV{PERL_ANYEVENT_MODEL} }
1268 2063
1269 use AnyEvent; 2064 use AnyEvent;
1270 2065
1271 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can 2066 Similar considerations apply to $ENV{PERL_ANYEVENT_VERBOSE}, as that can
1272 be used to probe what backend is used and gain other information (which 2067 be used to probe what backend is used and gain other information (which
1273 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL). 2068 is probably even less useful to an attacker than PERL_ANYEVENT_MODEL),
2069 and $ENV{PERL_ANYEVENT_STRICT}.
2070
2071 Note that AnyEvent will remove *all* environment variables starting with
2072 "PERL_ANYEVENT_" from %ENV when it is loaded while taint mode is
2073 enabled.
2074
2075BUGS
2076 Perl 5.8 has numerous memleaks that sometimes hit this module and are
2077 hard to work around. If you suffer from memleaks, first upgrade to Perl
2078 5.10 and check wether the leaks still show up. (Perl 5.10.0 has other
2079 annoying memleaks, such as leaking on "map" and "grep" but it is usually
2080 not as pronounced).
1274 2081
1275SEE ALSO 2082SEE ALSO
1276 Utility functions: AnyEvent::Util. 2083 Tutorial/Introduction: AnyEvent::Intro.
1277 2084
1278 Event modules: EV, EV::Glib, Glib::EV, Event, Glib::Event, Glib, Tk, 2085 FAQ: AnyEvent::FAQ.
1279 Event::Lib, Qt, POE. 2086
2087 Utility functions: AnyEvent::Util (misc. grab-bag), AnyEvent::Log
2088 (simply logging).
2089
2090 Development/Debugging: AnyEvent::Strict (stricter checking),
2091 AnyEvent::Debug (interactive shell, watcher tracing).
2092
2093 Supported event modules: AnyEvent::Loop, EV, EV::Glib, Glib::EV, Event,
2094 Glib::Event, Glib, Tk, Event::Lib, Qt, POE, FLTK.
1280 2095
1281 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event, 2096 Implementations: AnyEvent::Impl::EV, AnyEvent::Impl::Event,
1282 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl, 2097 AnyEvent::Impl::Glib, AnyEvent::Impl::Tk, AnyEvent::Impl::Perl,
1283 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE. 2098 AnyEvent::Impl::EventLib, AnyEvent::Impl::Qt, AnyEvent::Impl::POE,
2099 AnyEvent::Impl::IOAsync, Anyevent::Impl::Irssi, AnyEvent::Impl::FLTK.
1284 2100
1285 Non-blocking file handles, sockets, TCP clients and servers: 2101 Non-blocking handles, pipes, stream sockets, TCP clients and servers:
1286 AnyEvent::Handle, AnyEvent::Socket. 2102 AnyEvent::Handle, AnyEvent::Socket, AnyEvent::TLS.
2103
2104 Asynchronous File I/O: AnyEvent::IO.
1287 2105
1288 Asynchronous DNS: AnyEvent::DNS. 2106 Asynchronous DNS: AnyEvent::DNS.
1289 2107
1290 Coroutine support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event, 2108 Thread support: Coro, Coro::AnyEvent, Coro::EV, Coro::Event.
1291 2109
1292 Nontrivial usage examples: Net::FCP, Net::XMPP2, AnyEvent::DNS. 2110 Nontrivial usage examples: AnyEvent::GPSD, AnyEvent::IRC,
2111 AnyEvent::HTTP.
1293 2112
1294AUTHOR 2113AUTHOR
1295 Marc Lehmann <schmorp@schmorp.de> 2114 Marc Lehmann <schmorp@schmorp.de>
1296 http://home.schmorp.de/ 2115 http://anyevent.schmorp.de
1297 2116

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